16 PHYSIOLOGY CHAP. 



The total quantity of carbon eliminated comes either from the 

 protein, fat, or carbohydrates. The average proportion between 

 the nitrogen and the carbon in the protein being, according to 

 the researches, made by Kubner, as 1 : 3'28, it follows that in 

 the combustion of all the protein 3*28 x 16'2, that is, 531 grms. 

 of carbon, were involved. The total quantity of carbon found 

 in the gaseous products of the pulmonary and cutaneous respiration 

 and in the urine amounted to 219'6 grms. of carbon ; we have 

 therefore 166'5 grms. of carbon to distribute among the non- 

 nitrogenous food substances, that is, the fats and carbohydrates. 



If we knew the total amount of oxygen consumed during the 

 experiment it would be easy to deduce from the value of the 

 respiratory quotient whether the material deposited consisted 

 of fat or carbohydrate. The problem can, however, be solved 

 fairly accurately by simply taking into account the composition 

 of the diet and the faeces which pertain to it. Many researches 

 have indeed proved that during metabolism carbohydrates are 

 burnt more quickly and readily than fats. We may then 

 legitimately assume that the remaining 166'5 grms. of carbon are 

 derived from the carbohydrates absorbed, and that any excess 

 over their content of carbon may be reckoned as fat consumed. 



The carbohydrates absorbed amounted, as already stated, to 

 186'6 grms. which contain 124'7 grms. of carbon. There is then 

 a remainder of 41*8 grms. of carbon derived from the combustion 

 of fat, that is to say, that in addition to all the carbohydrates, 

 54'6 grms. of fat have been burnt. 



We therefore conclude that the subject of the experiment 

 consumed daily an average of 101'5 grms. of protein, 286'6 grms. 

 of carbohydrate, and 34'6 grms. of fat. If we compare the 

 intake and output, we find that the individual in question lost 

 about 12 grms. of protein and gained about 24 grms. of fat. 



A perfect equilibrium between the intake and output of 

 material, so that the weight of the body remains unchanged, does 

 not obtain. Even under the most regular and uniform physio- 

 logical conditions in adults the equilibrium is unstable ; the 

 weight varies slightly from day to day, from week to week. 

 There is a dynamic equilibrium ; certain chemical components 

 of the organism are consumed and are replaced by others derived 

 from the food. That the components thus substituted are not 

 identical either as regards quality or quantity with those which 

 are decomposed is proved by the fact that the composition of the 

 body even when its weight is only subject to slight positive or 

 negative variations changes slowly and constantly with age. 



IV. The total amount of the exchange of material varies 

 considerably with varying conditions, but is mainly dependent 

 on the quantity and quality of the food taken. When, therefore, 

 the subject is deprived of food, we have the simplest case of 



