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2 A NOTE ON THE SPECIFIC GRAVITY OF THE LIVING HUMAN BODY BY PRANK SANDON, M.A. I. INTRODUCTION IN Biometrika() an account was given of experiments based on Archimedes principle for the determination of the density of the living male human body. These were conducted on schoolboys in a freshwater indoor swimming bath; the sinkers used were lumps of iron (7 or 0 lb. dumbbells, domestic flatirons, or commercial weights) and the apparent weight was recorded by means of a spring balance (reading to lb. by ounces, or to 0 lb. by 2 oz.). These experiments were originally performed to settle some of the fundamental facts in connection with the possibility of floating as understood by swimmers. An outline of the conclusions has recently been published in the Swimming Times(z), but the experiments possess some scientific interest and a report of the work is therefore appended below: it deals with the experiments recorded in Biometrilca, some similar experiments not previously reported, and surveys the results to date.. METHOD The subjects were invited to attend at a London indoor freshwater swimming bath, or openair freshwater bathing pond. They were usually swimmers personally acquainted with the writer or with his father, or introduced by leading English swimmers interested in the experiments. Where possible, in addition to the name, age, sex, height and weight of the subject, there were recorded the apparent weight in water with lungs fully inflated, apparent weight in water after deep expiration, and the capacity of the subject to float, i.e. to remain motionless on the surface of water.. A CHECK ON THE METHOD Both the apparent weights were recorded in 0 cases. After a deep inspiration the volume of the body exceeds that recorded after a deep expiration by an amount equivalent to the vital capacity of the subject, since the subject in the former case displaces a corresponding amount more of fresh water, and thus reduces his apparent weight by the weight of a volume of water equal to that of the vital capacity. As lb.=weight of 28 cu. in. of fresh water, the following frequency table (Table I) in lb. can readily be converted into Cu. in. by multiplying the measure of the weights by 28. The modal value is 6 lb. (2 cases), equivalent to a vital capacity of 68 cu. in. This is slightly below the commonly accepted value as determined by a spirometer. This is what we should expect. For if a swimmer be asked to immerse himself with his lungs fully inflated he will

3 ~ ~ ~~~~ FRANK SANDON 7 inhale deeply, and then, by force of habit, exhale slightly to effect the immersion. On the other hand, if he be asked to immerse himself with lungs fully deflated, he will, after exhaling, inhale slightly lest he lose his breath under water. Together these two effects reduce the difference between the two cases. We may note, further, that some of the other cases not included in the 0 below found the expiration test impossible, whilst we were limited to using swimmers, as nonswimmers had not sufficient confidence to allow themselves to be immersed at all. The sample tested was thus selected by force of circumstances as one composed of swimmers interested in the question of floating, and possibly thus comprising an undue proportion of such who found that despite practice they could not float, although they had sound mastery in the water otherwise. Among swimmers generally, observation does not seem to suggest that there is any association between ability to swim Males of age: andover Females l I. Table I Change of apparent weight, in lb., between deep inspiration and deep expiration i i well and ability to float well. In learning to swim, however, confidence is necessary, and this is undoubtedly assisted by buoyancy. I cannot say how on the balance these two tendencies in sampling () by those able to swim and (2) by choosing, of these, those not able to float, would make our sample differ from a random one. IV. THE CALCULATED SPECIFIC GRAVITIES The water was in all cases fresh and at a temperature of between 60 and 75 B., i.e. of a density of As thirdfigure accuracy in the determination of the specific gravity of the human body,is impossible by the method used, no correction is necessary for the deficiency of the specific gravity of the water below.00. The stripped body weight was recorded in 59 cases, and the specific gravity thus computed. The frequency table (Table IIA) gives the results of the specific gravity of the living body for these cases after the deepest inspiration possible under the conditions of the experiment. The results may be summarised as shown in Table IIB.

4 7 SPECIFIC GRAVITY OF THE LIVING HUMAN BODY Males of age: and over 0.92 i i 2 Table I A Specific gravity I / males I 7 I : I 0.99 i Females : and over 2 i ~ females Table I B Group Number Mean sp. gr. S.D. M. 0 M.2 M M. 6 I M. 8 I M. 20 I M. 0 IM.0 59 F F V. DISCUSSION OF THE RESULTS The data are limited, and full analysis is unnecessary, but the results strongly suggest the following : (a) Specific gravity, like other anthropometric measures, is distributed according to a frequency curve that, judging by the population sampled, is roughly normal, with, however, a tendency to skewness so that it tails out to the lighter end. (b) The specific gravity of the female body is definitely less than that of the male, in fact, the densest woman observed is as light as the median man. (c) The specific gravity of the human body increases through adolescence, but after the twenties have been passed begins to get less again. (d) The specific gravity of various individuals of any particular age group varies somewhat widely, but this scatter is less pronounced in early manhood than at other times. VI. BEARING OF THE RESULTS ON THE QUESTION OF THE ABILITY TO FLOAT To float, the human body lies quietly on the surface of the water. As the adult subject breathes quietly exchanging tidal air, and thus varying his apparent weight by about lb., he rises and sinks in the water. After a quiet expiration a fresh inspiration can be

5 BRANK SANDON 75 made if the mouth is above water at this stage. For this to be possible with an adult it is necessary that there should be the exposure of at least 0cu. in. (say, Ocu. in. face, 0 cu. in. chest, and 0 cu. in. for fingers, toes and knees) or a residual buoyancy of another lb. Thus to float such an adult will need an apparent weight of 2 lb. less than that of the displaced water after a nominal full inspiration. Assuming that the forced inspirations in our case were incomplete, as is probableviolent breathing would, for one thing, cause far too much vertical oscillation of the bodyand that only onethird of the possible 00 cu. in. of complemental air were used, then we have, that, to float, our adult would show an apparent weight of about lb., or, if his weight be 50 lb. (0 st. 0 lb.), a specific gravity under the conditions of our experiment of This is borne out by Table I for 97 individuals (mostly adults, butnot all included in the 0 or the 59 already referred to) for which a record of their power to float is given. Table I Number of individuals who said, re floating in fresh water, Cannot Can just or can vertically or can nearly Can* For lungs supposedly fully inflated, apparent weight less (or more) than that of an equal volume of water Less 8 7 6? 5 ~ More * We may observe that all those who had their apparent weight well below that of an equal volume of water were recorded, if at all, as good plungers, i.e. could maintain, face downward, a horizontal impetus given by a takeoff until all momentum waa lost. Many, in attempting to plunge, fail: the legs first, and then the whole body, sink. The overlap between the three classes arises in one or more of four possible ways: (a) Experimental errors in reading the scale of the spring balance. (b) Failure on the part of the subjects always to inflate to the same degree. (c) Ignorance on the part of the subjects of their floating ability, or failure to practise. (d) Error involved in considering here apparent weight in place of specific gravity, the 97 subjects having different actual body weights. It follows that if we accept, say, (see later) as the maximum specific gravity that anyone should have if he is to float in fresh water, then (a) All females, girls and women alike, can float in fresh water. (b) The large majority of boys under, and of men over 0, can float. (c) A large proportion, nearly 50 per cent. at age 5, of adolescent boys will not be able to float.

6 76 SPECIFIC GRAVITY OF THE LIVING HUMAN BODY It further follows that: (d) Practically every male can float in sea water. For this is, in the case of the North Atlantic, of density.026, and, using the method of paragraph VI above and of (e) below, a human body of specific gravity less than.0, as practically all are, could float in it. (e) That, by control of breathing and by exchanging a certain amount of complemental air in place of tidal air in respiration, men of specific gravity may, in quiet water and if well proportioned physically, learn to float. This modification by learning is only possible to a small extent, and in consequence the observation only applies to a very few individuals. But those adults whose apparent immersed inflated weights range between 2 lb. and lb., say, and thus are of specific gravity , if well built, may learn to float with persistent and welldirected practice. VII. SUMMARY AND CONCLUSIONS A method is described of determining the specific gravity of the living human body. The modal value is 0.98 for the male. A rough survey is made of the age, sex and individual variations, especially in relation to the ability to float motionless in fresh water. REFERENCES () SANDON, FRANK (92). A preliminary inquiry into the density of the living male human body. Biometrika, 6, 00. (2)(95). This floating business. Swimming Times (, Waddon Park Avenue, Croydon),, 669.