(Received 10 June 1950)

459 J. Physiol. (I95I) II2, 459-475 THE LOSS OF HEAT FROM THE HANDS AND FROM THE FINGERS IMMERSED IN COLD WATER BY A. D. M. GREENFIELD, J. T. SHEPHERD AND R. F. WHELAN From the Department of Physiology, The Queen's University of Belfast (Received 10 June 1950) The calorimetric method has recently been applied (Greenfield & Shepherd, 1950) to the study of the vasodilatation induced in the finger tip by immersion in cold water (Lewis, 1930). In the course of these observations it was found that the heat loss from the terminal 2X8 cm. of the index finger (hereafter called the finger tip) immersed in water at 0-6 C. varied in different subjects from 1100 to 3400 small calories (cal.)/100ml. of tissue/min. at the height of cold vasodilatation. During the first hour of immersion the total heat loss was as much as 3X8 large calories (kg.cal.). If, when the whole hand is immersed, the heat loss were proportional to that from the finger tip, it would in some persons amount to as much as 840 kg.cal./hr. However, there are reasons, considered later, for expecting the heat loss from the whole hand to be proportionately less than that from a single finger tip. The experiments now described show that this is in fact the case. Observations have been made on the heat loss from the whole hand, and also from the four fingers. METHODS The calorimeters used were of the vacuum jar type described by Greenfield & Scarborough (1949). The calorimeter employed in the 06 C. range had the electric heating coil disconnected; that employed in the 29-32 C. range had the coil in operation. In experiments where the whole hand was observed no other modifications were made. When the fingers onlv were observed, a transverse shelf was arranged 9 cm. below the under surface of the lid of the calorimeter (Fig. 1). A post, 8 cm. high, was erected on this shelf. The calorimeter was filled to the top of the post, a volume equal to that of the fingers to be immersed was removed, and the fingers inserted until- the tip of the middle one rested on the shelf. The position of this finger tip on the shelf was maintained by a wire ring. When the fingers were in cold water and sensation numbed, this ring prevented the finger slipping off the shelf. The temperature of the calorimeter contents, registered by a thermo meter graduated in hundredths of a degree C., was recorded at intervals of 1 min. On the scale 10 C. measured 7-5 cm., and an attempt was made to estimate the temperature to a thousandth of a degree Centigrade. Observations of the heating rate of the calorimeter showed that our readings agreed within ±2 milli C. of the average rate. It was only necessary to measure differences of temperature with great accuracy. The actual temperatures could not, of course, be measured with comparable confidence.

460 A. D. M. GREENFIELD, J. T. SHEPHERD AND R. F. WHELAN Measurement of volumes offingers and hand. The volume of the fingers was measured by inserting them into a narrow oval vessel until the middle finger touched the bottom. The vessel was then filled to a depth of 8 cm., the fingers removed and the volume of water needed to restore the depth to 8 cm. was measured. The volume of the hand was measured by the method of Greenfield & Scarborough (1949). This method is accurate to ± 10 ml. (McCorry, 1950). Wall of Shelf Ring for 'thermos' suspended from finger tip jar top of jar Fig. 1. A section through the top of the calorimeter to show the four fingers in position, the middle finger resting on a shelf 8 cm. below the water level. The thermometer and stirrer are not shown. Mea8urement of the surface area of immersed tissue. Two methods were used: (a) A comfortably fitting rubber glove was marked at the various levels of immersion. It was then cut up and the parts which had been immersed were weighed. These weights were then compared with the weight of a known area from the same glove. The weights of equal areas from different parts of the glove agreed to within 5 %. (b) Adhesive plaster was carefully applied, and while in position marked at the various levels of immersion. It was then removed, cut up, and the parts weighed. A measured area of the same plaster was also weighed. In both cases areas were deduced from the weight of material.

HEAT LOSS FROM THE HAND 461 RESULTS Heat loss from the hands to water at 0-60 C. The standard procedure was to immerse the hand in a water-bath at 290 C. for at least 20 min. and then to dry it and transfer it to a calorimeter, the contents of which were at about 10 C. The other hand was similarly treated, but was inserted about 5 min. earlier into another calorimeter containing water at about 290 C. The measurements on this hand indicated the general level of vasomotor tone. Heat lossfrom a hand with the circulation arrested. The immersion of a hand with the circulation arrested in water at about 10 C. is extremely painful, and observations were made on two occasions only. The results of one of these experiments in which the subject kept his hand in the water for 11 min. are shown in Table 1. The rate of heat loss had fallen in the 8th min. to less than one-tenth of its value in the 1st min. The heating rate of the calorimeter was 12 milli C./min. in the period before immersion of the hand (Table 2, column 3). A constant correction of -12 milli' C. has been applied to the remaining figures in the column to obtain the temperature rise due to the immersed hand (column 4). No serious error is involved in assuming a constant heating correction. The results of this experiment, which are similar to those of the other comparable experiment, have been employed to arrive at the heat loss from the circulating blood in the main series of experiments. There are five difficulties in so employing these results: (1) Although the hands in this and in the other experiments were equilibrated with water at 29 C. for at least 20 mm., it is unlikely that at the end of this time the internal temperature of the hands was 290 C. (Barcroft & Edholm, 1943). It cannot even be assumed that the internal temperature was the same on different occasions, as it must have depended on the state of the circulation at the time. (2) Results obtained in this way on one person may not in fact be strictly applicable to other persons' hands. It is thought unlikely, however, that the thermal conductivities and specific heats of different hands vary enough to make this objection important. (3) No figures are available after the 11th min. when the heat output from the hand with the circulation arrested was 31 cal./100 ml./min. We have assumed that the heat loss continued at this rate, although in fact it must have fallen further. (4) In our calculations it is assumed that the hand cools to the calorimeter temperature. In fact it does not do so if the circulation is free. Even with the circulation arrested, the hand takes a long time to come into equilibrium with cold water in a calorimeter. For example, by the 6th min. (Table 1) the total heat output from 100 ml. of hand was 1126 cal., and by the 10th min. 1309 cal. Assuming a specific heat of 0-71 and a specific gravity of 1-13 (Stewart, 1911), one would expect 385 ml. of hand at 29 C., when inserted into 4000 g. of water

462 A. D. M. GREENFIELD, J. T. SHEPHERD AND R. F. WHELAN at 1.7410 C., to come into equilibrium at a final temperature of 3-690 C., the hand releasing 2031 cal./100 ml. in so doing. It follows that at the 6th min. the hand had given up only 55-4 % and at the 10th min. only 64-4% of the TABLE 1. Calorimetric observations on the left hand of R. F. W., with the circulation arrested. At - 1 min. the hand was removed from a water-bath at 29GC. with which it had been equilibrated for 20 min. and dried. At - 0.5 min. a cuff was inflated on the left arm to 250 mm. Hg. At 0 min. the hand was inserted in the calorimeter. Hand vol. 385 ml. Water equivalent of calorimeter and contents (other than immersed hand) 4000 g. Temperature rise Heat output from Calorimeter due to immersed immersed hand temperature Temperature rise hand (cal./100 ml. Time in min. (O C.) (milli C./min.) (milli C./min.) hand/min.) - 2 1-717 - 1 1-729 12 0 0 0 1-741 12 0 0 1 2-205 464 452 470 2 2-450 245 233 244 3 2-614 164 152 158 4 2-730 116 104 108 5 2-822 92 80 83 6 2-895 73 61 63 7 2-961 66 54 56 8 3-015 54 42 44 9 3-069 54 42 44 10 3-119 50 38 39 11 3-161 42 30 31 Observations discontinued at the 11th minute because of very severe pain. TABLE 2. Calorimetric observations on the left hand of R. F. W., with the circulation free. At - 1 min. the left hand was removed from a water-bath at 290 C. with which it had been equilibrated for 30 min. and dried. At 0 min. it was inserted in the calorimeter. Hand vol. 450 ml. Water equivalent of calorimeter and contents (other than immersed hand) 4000 g. Time in min. -2-1 01 2 3 4 56 7 8 9 10 11 12 Calorimeter temperature (O C.) 0-600 0-612 0-625 1-100 1-400 1-585 1-718 1-836 1-941 2-071 2-245 2-465 2-739 2-990 3-240 Heat output Heat output Temperature from immersed due to blood Temperature rise due to hand (cal./ flow (cal./ rise immersed hand 100 ml. hand/ 100 ml. hand/ (milli C./min.) (mill C./min.) min.) min.) 12 13 475 300 185 133 118 105 130 174 220 274 251 250 0 0 463 288 173 121 106 93 118 162 208 262 239 238 0 0 412 256 153 109 94 82 105 144 186 233 213 212 0 0 ( -58) 12 ( -5) 1 11 19 49 100 142 194 182 expected total. The average internal temperature of the hand at the 6th and at the 10th min. were, by calculation, 14-9 and 12.60 C. respectively. Thus the hand equilibrates much more slowly than the finger tip, which was found by

HEAT LOSS FROM THE HAND 463 Greenfield, Shepherd & Whelan (1950) to come within 2% of equilibrium by the 7th min. It follows from this that the heating of the hand by warm blood commences at a time when the hand is still considerably above the calorimeter temperature. The amount of heat derived from the cooling of the hand with the circulation free (omitting any heat from circulating blood) is therefore less than that derived from the cooling of the hand with the circulation arrested; in the former case the hand does not cool to so low a temperature as in the latter. 30 00 30 R.F.W. 200 20 0 220 0 ~~ ~~~~~~0 0 U Soo o 02 100 co 10 ~ 10-0 0 0 0 10 20 30 40 0 10 20 30 40 Minutes Minutes Fig. 2. The heat loss from the left hand of R. F. W. into a calorimeter in the 0-6' C. range (left rectangle) and from the right hand into a calorimeter in the 29-32O C. range (right rectangle). The left hand was transferred from water at 290 C. to the calorimeter at 0 min. On the left side, the upper line represents the total heat loss, and the black area the deduced heat loss from the circulating blood. Heat loss is expressed in cal./100 ml./min. The calorie scales differ on the two sides, but have been chosen so that the scales of minimum blood flow correspond. The minimum blood flows have been calculated as described in the text and are expressed in ml./100 ml./min. Pain is shown on a roughly quantitative scale at the top of the figure. The deduction we have made (Table 2, columns 5 and 6) for the heat due to the cooling of the hand is therefore too large, and it follows that on this count we underestimate the amount of heat derived from the circulating blood. (5) We do not know the amount of metabolic heat formed under the condition of our experiments. If we accept Stewart's (1911) figure of 5 cal./min. for the whole hand, it is clear that the metabolic heat is very small compared with the heat losses observed in our experiments. It is unlikely that the errors mentioned seriously upset our estimate of the heat derived from the circulating blood. They in no way affect our figures for the total heat loss from the hands.

O-60 C. 29-32 C. A.D.M.G. 060 C. 29-320 C. R. F.W. IN,i i J.T.S. M.F.R. Fig. 3. The heat loss from the hand of four normal subjects into water in the 0 60 C. range. The experiment on R. F. W. is the same as that shown with the scales fully marked in Fig. 2. The conventions in the other figures are the same. That is, on the 0 60 C. side the marks are at 500 and 1000 cal./100 ml. hand/min. and on the 29-32 C. side at 100 and 200 cal./100 ml. hand/min. In every case the full width of each rectangle represents 45 min. 0-6'C. 29-320C. Fig. 4. The heat loss from the distal 2-8 cm. of the index fingers of M. F. R. into water in the 0)60 C. range (left figure) and into water in the 29-320 C. range (right figure). The heat loss has been expressed in the same way as in Fig. 3 and the scales are identical.

HEAT LOSS FROM THE HAND 465 Heat loss from hands with the circulation free. In all experiments one hand was observed in a calorimeter at 29-32 C. (Cooper, Cross, Greenfield, Hamilton & Scarborough, 1949) before and during observations of the other hand in 0-60 C 29-320C. 29-320C. 0-6 C. R. F.W. 1~A'YL k~uul I. I A.R. Fig. 5. The heat loss from the four fingers of six normal subjects into water in the 06 C. range. The conventions are as in Figs. 2 and 3. A. D. M. G., R. F. W., J. T. S., left fingers cold; M. F. R., J. H. C., A. R., right fingers cold. a calorimeter at 0-6 C. The observations on the cold side in the initial period of a typical experiment are shown in Table 2. It can be seen that in the first 4 min. of immersion in the cold water, the amount of heat given off per 100 ml. of immersed hand was little different whether the circulation was free or arrested.

466 A. D. M. GREENFIELD, J. T. SHEPHERD AND R. F. WHELAN In the 1st and 3rd min. more heat was given off with the circulation arrested; it is difficult to explain these discrepancies, which were greater in this experiment than in most of the others. Clearly the blood flow must have been negligible during this period. After the 5th min. an increasingly large amount of heat was lost when the circulation was free, reaching a peak at 10 min. and then slowly declining. The experiment was terminated at the 28th min. because the calorimeter temperature had risen above 60 C., the limit of the thermometer scale. The results of this experiment are shown in Fig. 2. We do not know the temperature of the arterial blood arriving at the hand or of the venous blood leaving it. It is impossible therefore to calculate accurately the hand blood flow from the heat exchange. If we assume that the blood arrives at 370 C. and leaves at 00 C., we can arrive at a figure which we call the 'minimum blood flow' and which we are certain is less than the real blood flow (Greenfield & Shepherd, 1950). The second scale in Fig. 2 shows the minimum blood flow calculated on this basis. The results of this and three similar experiments are shown in Fig. 3. After immersing the hand in cold water the heat elimination from the circulating blood was small or negligible for about 5 min. and then rapidly increased. It reached a maximum by the 7th-lOth min. and then either declined slowly or remained fairly steady. All these experiments had to be ended when the temperature of the water in the calorimeter had reached 60 C. Pain started almost immediately after immersing the hand and was very severe until the heat elimination began to rise. Occasionally pain was absent during the remainder of the experiment, but more often a dull ache persisted or came on towards the end. The changes in heat loss on the control side in a calorimeter at 29-32 C. often reflected the changes on the cold side. The initial insertion of the hand into the cold water caused a transient decrease in the heat loss from the opposite hand, which we interpreted as being due to reflex vasoconstriction. The heat loss from unit volume of hand is much less than from unit volume of finger tip. Fig. 4 shows the heat loss from the finger tip of M.F.R. measured by the method of Greenfield & Shepherd (1950). This result is typical for a finger tip immersed in water at 0-6 C., and when compared with the result obtained for the whole hand of this subject (Fig. 3) shows that the maximum heat loss from the finger tip in cal./100 ml./min. was over 10 times greater than the maximum from the hand. The heat eliminationfrom thefingers to water at 0-6 C. The standard procedure was similar to that employed in the case of the hand. The hands were immersed in a water-bath at 290 C. for at least 20 min., dried, and the fingers inserted into a calorimeter containing water at about 10 C.

HEAT LOSS FROM THE HAND 467 The other hand was similarly treated, but the fingers were inserted about 5 min. earlier into another calorimeter containing water at about 290 C. TABLE 3. Calorimetric observations on the left fingers of A. D. M. G. with the circulation arrested. At - 2 min. a cuff was inflated on the left arm to 220 mm. Hg. At -1 min. the hand was removed from a water-bath at 290 C. with which it had been equilibrated for 20 min. and dried. At 0 min. the fingers were inserted into the calorimeter. Finger vol. 64 ml. Water equivalent of the calorimeter and contents (other than immersed fingers) 4170 g. Temperature Heat output from Calorimeter rise due to immersed fingers temperature Temperature rise immersedfingers (cal./100 ml. Time in min. (O C.) (milli C./min.) (milli C./min.) finger/min.) -3 1-715 - -2 1-736 21 0 0-1 1-757 21 0 0 0 1-781 24 0 0 1 1-955 174 152 990 2 2-070 115 93 606 3 2-141 71 49 320 4 2-198 57 35 228 5 2-240 42 20 130 6 2-280 40 18 117 7 2-315 35 13 85 8 2-344 29 7 46 Observations discontinued at the 8th minute because of severe pain. TABLE 4. Calorimetric observations on the left fingers of A. D. M. G. with the circulation free. At - 1 min. the left hand was removed from a water-bath at 29 C. with which it had been equilibrated for 20 min. and dried. At 0 min. it was inserted in the calorimeter. Finger vol. 64 ml. Water equivalent of calorimeter and contents (other than immersed hand) 4170 g. Temperature Heat output Heat output rise due to from immersed due to blood Calorimeter Temperature immersed fingers (cal./ flow (cal. temperature rise fingers 100 ml. 100 ml. Time in min. (O C.) (milli0 C./min.) (milli C./min. finger/min.) finger/min.) -4 0-780 - 3 0-799 19 0 0 0-2 0-815 16 0 0 0-1 0-837 22 0 0 0 01 0-855 18 0 0 0 1-048 193 174 1134 144 2 1-180 132 113 736 130 3 1-249 69 50 326 6 4 1-306 57 38 248 20 5 1-359 53 34 222 92 6 1-406 47 28 182 65 7 1-479 73 54 352 267 8 1-582 103 84 547 501 9 1-710 128 109 710 710 10 1-872 162 143 932 932 11 2-020 148 129 841 841 12 2-195 175 156 1016 1016 Heat loss from the fingers with the circulation arrested. It is nearly as painful to immerse the fingers in water at about 10 C. as it is to immerse the whole hand. Observations were made on one occasion only, and the results are shown PH. CXII. 30

468 A. D. M. GREENFIELD, J. T. SHEPHERD AND R. F. WHELAN in Table 3. The temperature rise due to the immersed fingers was 152 milli' C. in the 1stmi., but only 7 milli' C. in the 8th min., by which time it is estimated that the heat lost was 96% of the expected total quantity lost in attaining equilibrium. These figures have been used to calculate, in this and other subjects, the heat loss from the circulating blood. After the 8th min. it was assumed that all the heat lost from the fingers came from the circulating blood. The errors involved in the calculation are similar to those already discussed in the case of the hand. They are, however, relatively much smaller. They in no way affect our figures for the total heat loss from the fingers. Heat loss from the fingers with the circulation free. The fingers of one hand were observed in a calorimeter at 29-32 C. before and during observations on the other hand in a calorimeter at 0-6 C. The observations on the cold side in the initial period of a typical experiment are shown in Table 4. Experiments of this kind were carried out on six subjects and the results are shown in Fig. 5. Observations were usually continued until the temperature of the calorimeter had reached the limit of the thermometer scale, but in one case (A. R.) they were stopped because of a vasovagal attack after immersion in the cold water for 17 min. The heat loss from circulating blood was negligible for the first 5 min. A very rapid increase in the rate of heat loss followed in all cases, and reached a peak at about the 10th min. The subsequent pattern varied from subject to subject. Usually there was a slow decrease in heat loss interspersed with temporary increases. As in the hand, pain was severe when the rate of heat loss was low, and absent or slight when it was high. The initial insertion of the fingers into the cold water caused a transient decrease in the heat loss from the fingers of the opposite hand. Heat loss from thefingers under different environmental conditions The heat loss from the fingers of one of these subjects (J. T. S.) was determined on three separate occasions under three different environmental conditions. These were: (a) Almost naked in a cold room with two electric fans directed towards the body and with both feet and calves in iced water. The whole length of each arm down to the fingers was protected with heavy wool scarves in order to prevent extra pre-cooling of the arterial blood. (b) Normally clothed in a room at 210 C. (c) Wrapped in blankets in a room at 230 C. with the feet and calves in a stirred water-bath at 440 C. The results of these three experiments are shown in Fig. 6. With the subject generally cold (upper rectangles, Fig. 6), while there was practically no heat loss from the fingers in a calorimeter at 29-320 C., indicating a state of peripheral vasoconstriction, a slight transient vasodilatation still occurred in the opposite fingers immersed in a calorimeter at 0-6' C. This was only sufficient, however, to cause a temporary reduction in the severe pain, and the experiment had to

0-60C. HEAT LOSS FROM THE HAND 29-320C. 0-60 C 0-6 C. 469 J.T.S. A.D.M.G. I Fig. 7. 0-60 C. 0-60C. Fig. 6. Fig. 8. Fig. 6. The heat loss from the four fingers of J. T. S. into water in the 0-6 C. range under three different environmental conditions. Top figure: almost naked in a cold room with two electric fans directed towards the body and with both feet and calves in iced water. The whole length of each arm down to the fingers was wrapped in heavy wool scarves. Middle figure: normally clothed in a room at 210 C. Lower figure: wrapped in blankets in a room at 230 C. with the feet and calves in a stirred water-bath at 440 C. The conventions are as in Figs. 2 and 3, but the height of the lower figure has been increased without changing the scales. Fig. 7. Simultaneous observations of the heat Joss from the four fingers of the right and left hands into water in the 06 C. range. The conventions are as in Figs. 2 and 3. Fig. 8. Simultaneous observations of the heat loss from the hands of A. D. M. G. into water in the 0 60 C. range. The conventions are as in Figs. 2 and 3. 30-2

470 A. D. M. GREENFIELD, J. T. SHEPHERD AND R. F. WHELAN be terminated after the 19th min. The maximum heat loss was 350 cal./100 ml. finger/mmn. With the subject comfortably warm (middle rectangles, Fig. 6) the heat loss following the initial decrease reached 460 cal./100 ml. finger/min., and varied between 300 and 480 throughout the remainder of the experiment. Under these conditions the fingers were painful for the first eleven minutes only. When the subject was very warm (lower rectangles, Fig. 6) the heat loss from the circulating blood was high in the first 5 min. It then fell, but never to zero, and at the 9th min. began to increase rapidly, reaching a value of 1580 cal./100 ml. finger/min. by the 16th min. The limit of the thermometer scale was reached at the 25th min. The pain was only severe in the 7th and 8th mins. and disappeared completely at the 10th min. From the 12th min. onwards the fingers on the cold side felt warmer than the opposite fingers which were in water at 29-32 C. Simultaneous observations of the heat loss on the two sides In two subjects the heat losses from the fingers of the right and left hands were compared simultaneously at 0-6o C. (Fig. 7). While there were slight dcwerences, the general behaviour was symmetrical. The response of the two hands of these subjects was also compared in the same temperature range (Figs. 8, 9) with similar results. In all these experiments, when the cold vasodilatation started, the pain in the fingers or hand became less severe or disappeared. At the same time a sensation of cold, and often of pain, was felt just above the water level, and mainly on the dorsum of the hand or wrist. This gradually spread up the arm; the pain usually subsided in a few minutes, but the sensation of cold usually persisted. The rate of heat loss showed that the circulation was completely or almost completely arrested for the first 5 min. Little or no cold blood would therefore return in the veins during this time. When the vasodilatation started, very cold blood would flow up the veins in large quantities. It seemed likely that this was th-e explanation of the sensations. To test this hypothesis the temperature of the skin over a prominent dorsal vein, about 5 cm. above the water level, was measured with a thermoelectric junction held in place by one layer of adhesive plaster; one junction was on the side with the fingers or hand in water at 0-6O C. and another on the control side at 29-32 C. In seven experiments on six subjects the temperature on the control side remained at a more or less constant level about 290 C. throughout the experiment. On the side with the fingers or hand in the calorimeter at 0-6 C., the temperature remained nearly constant at about 290 C. during the initial period, when the measurements of heat loss showed that blood flow was very small. It then dropped sharply to 15-190 C. over the next 5-11 min. as the cold vasodilatation started and the calorie output increased. This drop in temperature was ac-

HEAT LOSS FROM THE HAND 471 companied by a sensation of cold and often of pain in the dorsum of the hand. During the remainder of the experiment the temperature fell a further 2-3' C. In one of the two experiments in which both hands were immersed in calorimeters at 0-6' C. recordings were made of the oesophageal temperature as well Time in minutes Fig. 9. Simultaneous observations of the heat loss in cal./100 mj./min. from the two hands of R. F. W. into water at 046 C. The temperature of a thermoelectric junction applied to the skin over a vein on the dorsum of each wrist is shown below the graph of heat loss from the corresponding hand. The temperature of a thermoelectric junction in the oesophagus 40 cm. from the incisor teeth is shown at the bottom. as of the skin temperature over a large wrist vein on each side. The former was measured by a thermoelectric junction in the end of a Ryle's tube 40 cm. from the incisor teeth. Readings were accurate to + 0.03 C., and the system was calibrated before and after the experiment. The results are shown in Fig. 9. During the initial period, when the pain was at its maximum and the heat loss

472 A. D. M. GREENFIELD, J. T. SHEPHERD AND R. F. WHELAN from circulating blood negligible, the skin and oesophageal temperatures remained unchanged. At the 5th min., when the heat loss indicated vasodilatation, the pain left the hands and moved into the wrists and arms which now felt cold. At the same time the temperature of the skin over the wrist veins began to drop, falling 100 C. in 4 min. At the 7th min. the oesophageal temperature began to fall from 36.50 C., reaching 35.950 C. 8 min. later. This shows that a large volume of cold blood was returning to the body. The oesophageal temperature rose from the 15th min. until the end of the experiment, when it was 36.10 C. There was no shivering, but the subject felt an involuntary increase in muscle tension which may have contributed to this small rise in temperature. A comparison of the heat elimination from the finger tip, fingers and hand at the height of cold vasodilatation Fig. 10 shows the heat losses in calories per minute from the whole hand, the four fingers of one hand and one finger tip when immersed in a calorimeter at 0-6 C. All figures refer to heat loss at the height of cold vasodilatation. The values for the finger tip are taken from a previous paper (Greenfield & Shepherd, 1950). Little more heat is lost from the whole hand than from the four fingers, but the whole hand loses about eight times as much heat as does a single finger tip. In Fig. 11 the same results are shown, but the heat loss has been expressed in cal./100 ml. tissue/min. It is clear that the finger tip loses more heat per unit of volume than do the four fingers. The four fingers in turn lose more heat than does the whole hand. In one subject (J. T. S.) the surface areas of the immersed parts have been measured by the two methods already described. These showed respectively that the distal 2 8 cm. of index finger was 2-85 or 2 7 % of the total area of the hand, and that the area of the immersed parts of the four fingers was 30 or 27-7 % of the total area of the hand. The averaged results by the two methods were, for the finger tip 14-5 sq.cm., for the four fingers 151 sq.cm., and for the whole hand 523 sq.cm. The heat losses to water at 0-60 C. at the height of cold vasodilatation in this subject were for the finger tip 6-9, for the four fingers 2-45, and for the whole hand 141 cal./sq.cm./min. The finger tip, therefore, loses more heat per unit of area, as well as per unit of volume, than do the four fingers; these in turn lose more heat than does the whole hand. DISCUSSION The heat loss from the terminal 2-8 cm. of the index finger immersed in water at 0-6' C. varies at the height of cold vasodilatation from 1100 to 3400 cal./ 100 ml./min. (Greenfield & Shepherd, 1950). If, when the whole hand is immersed, the heat loss were proportional to that of the finger tip, it would amount on the average to 530, and in some persons to as much as 840 kg.cal./hr.

HEAT LOSS FROM THE HAND 473 In fact, however, at the height of cold vasodilatation we find that the average heat loss from the four fingers is only 36, and from the whole hand only 90 c 4) L- o u 1V 60 ' -) v 4A 30.~ 0 v e 30 A.D.M.G. J.T.S. R.F.W. M.F.R. J.H.C. A.R. Fig. 10. The heat losses from (a) the whole hand (black columns), (b) the four fingers (oblique hatching) and (c) the distal 2*8 cm. of the index finger (clear columns) of six normal subjects. Heat loss is expressed in small cal./min. (not small cal./100 ml. tissue/min.) and in kg.cal./hr. A.D.M.G. J.T.S. R.F.W. M.F.R. J.H.C. A.R. Fig. 11. The heat losses from (a) the whole hand (black columns), (b) the four fingers (oblique hatching) and (c) the distal 2-8 cm. of index finger (clear columns) of six normal subjects. Heat loss is expressed in small cal./100 ml. of tissue/min. 48 kg.cal./hr. There are two main reasons for these differences. First, the circulation through the fingers is capable of passing a great deal more blood

474 A. D. M. GREENFIELD, J. T. SHEPHERD AND R. F. WHELAN per unit volume per minute than that through the whole hand (Wilkins, Doupe & Newman, 1938). Secondly, more heat may be lost from unit volume of blood passing through the finger than through the hand. The absolute quantity of heat lost from a single finger tip is only about one-eighth of that lost from the whole hand (Fig. 10). The returning venous blood from a single finger tip may therefore be expected to cause less cooling of the arm and hence less pre-cooling of the arterial blood. There is no doubt that the fingers and the whole hand are capable of cold vasodilatation. The extent of the response is modified by the level of peripheral vasodilatation or constriction as judged by the heat loss from the control side. It still occurs, however, in spite of marked general vasoconstriction due to cooling of the body as a whole (Fig. 6). Without an accurate knowledge of the temperature of the blood entering and leaving the hand when immersed in water at 0-6 C. we cannot translate figures for heat loss into actual blood flow. The minimum figures we have calculated (Fig. 2) on the basis of blood arriving at 370 C. and leaving at 00 C. are almost certainly much too small. Bazett, Love, Newton, Eisenberg, Day & Forster (1948) have recorded temperatures as low as 21.50 C. in the radial artery of a subject in a room at 90 C. This suggests that in our experiments the temperature in the radial artery on the cold side may have been well below 370 C. The temperature of the skin over the dorsal veins (Fig. 9) suggests that the temperature of the blood leaving the hand was considerably above 00 C. Measurements of heat loss when the hands or the fingers are immersed in water at 0-60 C. suggest that there is initially almost complete arrest of the circulation, followed, after 5-7 min., by a large flow of blood. This deduction is supported by observation of the oesophageal temperature and of the skin temperature over the dosal veins proximal to the immersed area. Because of the thermal lag of the system, the actual rate of change in blood flow is probably much greater than would appear from the figures. The thermal lag is mainly in the immersed tissues. The calorimeter and thermometer settle within one minute at a new temperature after a suddenly imposed temperature change. The release of heat from the hand (Table 1) or from the fingers (Table 3) is much slower. The pain on immersing the whole hand in cold water was worse but not very much worse than when one finger tip was immersed. It still bore the same relationship to the heat loss from circulating blood as it did in the case of the tip of the index finger (Greenfield & Shepherd, 1950). That is, pain was felt when the loss was low and not when it was high. SUMMARY 1. A method is described for measuring the heat loss from the fingers or from the whole hand into water between 0 and 60 C.

HEAT LOSS FROM THE HAND 475 2. A comparison of the heat loss with the circulation free and arrested enables the heat loss from the circulating blood to be calculated. The uncertainties in the calculation are discussed. 3. There is very little heat loss from circulating blood during the first 5 min. of immersion; the heat loss then rapidly rises to a high value, averaging at the height of cold vasodilatation, 200 cal./100 ml./min. in the hand and 877 cal./ 100 ml./min. in the fingers. The corresponding figure for the distal 2-8 cm. of the index finger has previously been found to be 2200 cal./100 ml./min. 4. The average heat loss from one hand at the height of cold vasodilatation is at the rate of 48 kg.cal./hr., and from the fingers of one hand, 36 kg.cal./hr. Previous observations have shown that the average loss from the distal 2-8 cm. of the index finger is 6 kg.cal./hr. 5. In one subject, heat loss per sq.cm. was calculated at the height of cold vasodilatation from the tip of one finger (6.9 cal./min.), the four fingers (2.45 cal./min.) and the whole hand (1.1 cal./min.). 6. The heat loss is reduced when the subject is generally cold, and increased when he is hot. 7. The heat loss from the hands or fingers of a subject is symmetrical. 8. The returning venous blood during cold vasodilatation may reduce the temperature of the skin overlying veins proximal to the immersed part by as much as 100 C. in 4 min. When both hands are immersed, the oesophageal temperature may fall 0.550 C. in 8 min. 9. The relationship of pain to these events is described. 10. The results show that, at the height of cold vasodilatation, the blood flow must be not less than 5.5 ml./100 ml. hand/min. and not less than 24 ml./100 ml. fingers/min. The flows are probably much greater than this, but the available information does not permit a quantitative comparison with the maximum blood flow obtainable by other methods of vasodilatation. We wish to thank the students who acted as subjects for some of the experiments. The thermometers were supplied by Messrs B. Black and Son Ltd., 180 Goswell Road, London, E.C. 1. REFERENCES Barcroft, H. & Edhoim, 0. G. (1943). J. Physiol. 102, 5. Bazett, H. C., Love, L., Newton, M., Eisenberg, L., Day, R. & Forster, R. (1948). J. appl. Phy8iol. 1, 3. Cooper, K. E., Cross, K. W., Greenfield, A. D. M., Hamilton, D. McK. & Scarborough, H. (1949). Clin. Sci. 8, 217. Greenfield, A. D. M. & Scarborough, H. (1949). Clin. Sci. 8, 211. Greenfield, A. D. M. & Shepherd, J. T. (1950). Clin. Sci. 9, 323. Greenfield, A. D. M., Shepherd, J. T. & Whelan, R. F. (1950). Clin. Sci. 9, 349. Lewis, T. (1930). Heart, 15, 177. McCorry, R. L. (1950). Personal communication. Stewart, G. N. (1911). Heart, 3, 33. Wilkins, R. W., Doupe, J. & Newman, H. W. (1938). Clin. Sci. 3, 403.