THE MUSCULAR MOTOR AND ALIMENTATION 137 



2. Fats. These are oils, butter, and animal and vegetable 

 fats. A fat is a composition representing the union of a fat acid 

 with glycerine. Thus " stearin " is a combination of stearic acid 

 and glycerine. 



The co-efficient of digestibility of fats is from '90 to *97 ; the 

 average calorific power being 91 calories. For equal weights, 

 fats are the most exothermic substances. 



3. Proteids. These bodies, of the nature of albumen or white 

 of egg, exist in, milk (casein), cheese, also in meat, beans, peas, 

 lentils, etc. These are quaternates, because of the inevitable 

 presence of azote. The living matter- the protoplasma is 

 essentially nitrogenized. 



Their co-efficient of digestibility varies from -68 to -98 accord- 

 ing to the aliment considered its average value being -91 : it is 

 low in the vegetable aliments. 



The average calorific power is practically the same as that of 

 the carbo-hydrates 4T Calories. 



Comparing the calorific powers, in inter-organic combustion, 

 of 1 gramme of food, and the heats ot combustion, according to 

 Berthelot and Andre, the following average results are obtained. (*) 



NATURE OF ALIMENT CALORIFIC HEAT OF 



POWER COMBUSTION 



1 gramme carbo hydrates 4TO calories 4-20 calories 



1 of fats 9-10 940 



1 ofproteids 4-10 4-75 



Rubner ( 2 ) obtained as calorific powers : 4 TO cal, 9-30 cal. and 

 4-10 cal. ; Atwater and Bryant, 4 cal. 8-90 cal, 4 cal. 



Atwater and his collaboraters ( 3 ) determined the heat of inter- 

 organic combustion of the habitual aliment as a mixture ; they 

 estimated the heats of combustion per gramme at 4-10 cal. ; 9-40 

 cal., and 4-40 cal. ; these values have been verified by Kintaro 

 Oshima ( 4 ) who obtained identical results except for the carbo- 

 hydrates, for which he gave a value ol 4-20 cal. All these ex- 

 periments show that, in the organism, the proteid matter, reduced 

 by combustion to the state of urea, is not as exothermic as Berthe- 

 lot assumed. 



( x ) A "bomb" calorimeter (see 35) is used with oxygen under a 

 pressure of 25 atmospheres (Berthelot and Andre, Ann Chimie et Physique, 

 1891, vol. xxii., p. 25). 



( 2 ) Rubner (Zeitsch. f. Biol., vol. xxi., p. 377, 1885 ; xlii., p. 268, 1901). 



() Atwater and Bryant (Bull., No. 109, p. 86, 1899). 



(*) Kintaro Oshima (Bulletin, No. 159, p. 223, 1905). 



