--ET. ... rechnlques FOR DETERNlNlNG 'SPECIFIC GRAY1 T Y OF 1 I YE A N I H A L ' S 133.

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1 133 rechnlques FOR DETERNlNlNG 'SPECIFIC GRAY1 T Y OF 1 I YE A N I H A L ' S A Ha PEARSON M I C H I GAN S T A T E C O L L E G E The use of specific gravity i n determining body composition i s based on the promise that the major body components namely lean, bone, water and fat d i f f e r i n density Vierordt (1906) reported t h e panniculus a d i osus has a specific gravity of 0971 compared t o (range t o f o r s t r i a t e d muscles and t o 1717 f o r t h e bony cranium Various investigators (Ashworth and Cowgill, 1938; Pace and Rathbun, 1945; McNaUy, 1955) have shown body composition t o be r e l a t i v e l y constant when reduced t o the f a t - f r e e basis f o r rats, guinea pigs and chickens Pace and a t h b u n (1945), working with guinea pigs, reported water and nitrogen contents Were r e l a t i v e l y constant f r a c t i o n of l i v e weight when expressed on t h e fat-free basis with average values of and 352 per cent, respectively From such evidence the so-called "lean body mass" concept was developed, which i n essence states t h a t the gross chemical composition of the body is r e l a t i v e l y constant with fat acting as a diluent agent --ET - - There are some indications (Page and Babineau, 1953; Light e t al, 1934; Annegers, 1954) that abnormal conditions such as withholding water or subjecting anfmals to cold w i l l upset t h e normal balance of body water and fat Water Dispiacement Method Early work on specific gravity dates back t o Robertson i n 1757 reviewed by Boyd (1933) Attempts were made t o determine specific gravity of human subjects by submerging t h e body i n water This method i s based on the Archimedean principle t h a t the body immersed i n water loses weight by an amount equal t o the water displaced by it The early attempts of Robertson were unsuccessful due t o failure t o correct t h e weight of the submerged body f o r air i n the lungs and air passages Vierordt (1906) quoting t h e work of Krause f o r values obtained with a so-called "normal adult man" reported a specific gravity of after a moderate expiration, but when corrections were msde f o r a i r in the lungs and f o r gas in the intestines, t h e value rose t o Successful application of the water displacement method of determining specific gravity as a measure of fatness for human subjects i s credited t o Behnke ( ) He estimated the specific gravity of the human body, including f l u i d s and s o f t tissues, bone and e s s e n t i a l l i p i d s, but excluding "excess fat" at 1099 The addition of excess adipose tissue i n the amounts of 10, 20 or 333 per cent of the t o t a l body weight was calculated t o give specific gravity values of 1080, 1062, and 1036 respectively Behnke e t al (1942) described t h e method they used in determining the specific gravity of human subjects by underwater weighing Weights were

2 134 taken with a spring balance scale t o the nearest ounce by means of a l i n e from t h e subject t o the balance A weighted lead belt was used t o maintain negative buoysncy f o r a l l types of persons In order t o make necessary calculations and corrections f o r air i n the lungs and respiratory passages, it was necessary t o weigh once at the end of m&ximnrm inspiration and again a t the end of asximum e w i r a t i o n The difference in the two weights records hydroststic displece~uent, which serves as a measure of vital capacity By correction f o r the e f f e c t of mean hydrostatic pressure on the thoracic volume, values comparable t o those obtsined by standard spirometry methods a r e possible The following problem taken from t h e i r data will tend t o illustrate the principle: Wt i n a i r Wt i n H20 Wt i n HzO 183 lbs full inspiretion 142 lbs f u l l elrpiratlon Vital capacity - computed from volume a0 displaced 4090 cc 1200 cc 1375 lbs colqputed V o l m residual air W t of b e l t 232 lbs Correct ions =lied 232 l b s Wt of b e l t (in %O) 1375 l b s Gross W t minus w t of belt 94S lbs Corrected f o r residual air (1200/453) 265 l b s Corrected W t in H Gross w t i n H20 Wt in Air Specific Gravity - Wt z i n H20 in Air Volume = E Body Volume z Behnke e t al (1942) and Welham and Behnke (1942) presented data showing the relationship between certain physical measurements and specific gravity f o r the human as measured by water displacement Rathbun and Pace (1945) have evidence using eviscerated guinea pigs that the water displacement method i s valid %Costa sod Clayton (1950) using albino rats on different n u t r i t i o n a l l e v e l s bave verified the relationship between specific gravity and f a t content Correlations calcul8ted from DaCosta and Clayton's data by Brozek and Keys ( ) and reported i n their excellent review are r -073 for specific gravity and fat content of the carcass, and r = -087 f o r specific gravity arad water content of t h e carcass Unfortunately, the water displacement method has not been readily adaptable t o animsls other than man Not onjy i s the method cumbersome and

3 135 slow, but breathing cannot be readily controlled i n laboratory or farm animals However, the principles involved are sound Helium Dilution k t h o d This method makes use of the d i l u t i o n technique, i n which EL measured volume of helium is injected i n t o a chamber of known volume containing the experimental animal After allowing time f o r t h e gases i n t h e chamber t o reach equilibrium, a sample i s removed and analyzed f o r helium by a Cambridge Analyser, which u t i l i z e s differences in thermal conductivity of helium and dry air t o give t h e amount of helium This method has been described by Walser and Stein (1953) and they have reported good agreement between t h i s method and specific gravity as determined by water displacement of t h e eviscerated carcass S i r i (1953) simultaneously has reported successful r e s u l t s using the helium d i l u t i o n technique The exact d e t a i l s of t h i s method have not been published This method would appear t o be most promisiw f o r studying body composition of the i n t a c t animal Not only is the method adapted t o humans, but i n principle could be applied t o e i t h e r laboratory or farm animals A i r Displacement Method _ I Wedgewood and Newman (1953) have proposed an air displacement method for determining the specific gravity of the i n t a c t animal This method is based on the measurement of the volume of gas displaced by t h e animal body The method reported by Wedgewood and Ne(1953) has not been described i n detail, but as shown i n a picture by courtesy of the authors it apparently d e s use of bellows A t t h e Michigan Station, working i n cooperation with D r E P Reineke of our Physiology Department, we have been working independently on a similar principle Our device consists of two chambers of known volume connected together by means of rubber tubing with a vacuum pump and menometer linked i n t o t h e system The animal i s introduced into one chamber and a vacuum is drawn on t h e other chamber, which is closed off by means of a two-way stop-cock The amount of t h e vacuum i s recorded and t h e two chambers a r e connected Then by measuring t h e change i n pressure, e believe it is possible t o calculate the volume occupied by t h e animal W t h i s method i s sound i n principle, but t h e e f f e c t of a nmiber of variables, such as temperature of t h e chamber, vapor pressure and changes i n t h e gas content of the animal itself must be established before it can be applied with precision

4 136 L i s t of References Cited I Anaegers, J (1954) Proc SOC Expt Biol and Eaed 87:454 Ashworth, U S and Congill, G R (1938) Behnke, A R J Nutr l5:73 ( ) Harvey Lectures Ser Behnke, A R, Feen, B G and Welhm, W, C Assoc 118:495 Boyd, E (1933) Human Biol Brozek, J and Keys, A 5: 646 ( ) Nutr Abst DaCosta, E and Clayton, R 37:198 (1942) J h e r Med and Reviews, 20: 247 (1950) J Nutr 41:597 Li$ht, A E, Smith, P K, Smith, A, E, and Anderson, W E J B i d Cha 107: 689 MCNally, E H (1955) Poultry SCi Pace, N, and Rathbun, E N Page, E andbabineau, L, M, 34:152 (1945) J Biol Chem 158:685 (1953) Canad J Med Sci Reineke, E P and Pearson, A M (1934) 31:22 ( ) Unpublished data S i r i, W E (1953) Fed Proc 12:133 Vierordt, H (1906) batomtsche, Physiologische, and Physikalische Daten und Tabellen zum Gebrauch fiir Mediziner G Fischer, Jew Walser, M and Stein, S N (1953) Wedgewood, R J and NeMnan, R N Proc SOC Expt Biol and Med 82: 774 (1953) Amer J phys Anthropol 11:260 Welha, W C and Bebnke, A, R (1942) J Amer Med Assoc 118:498

5 137 Thank you, D r Pesrson, for t h a t fine presentation MR A U " : on technics f o r determining specific gravity of live animals A t t h i s time we w i l l hear from Professor C, P Wilder on "Probing as a Means of Determining Fatness (I EIR WIISER: Some time ago when I was assigned t h i s topic I figured it would be a cinch j u s t t o get up here and review some of the probing work Then I was t;olii t h a t it included t h e lean-meter which I had seen demonstrated but had never used So I think t h a t I have learned a l o t i n the last week, since I have been preparing t h i s talk both from t h e standpoint of review of the l i t e r a t u r e an8 from l e a r n i w t o use the leanmeter I tried the lean-meter on my fingers t h i s morning and it didn't r e g i s t e r Right a w I figured t h a t I wa6 dead But Ed Kline came over and assured me I was &live So I guess everything i s sll right