36 



PHYSIOLOGY 



CHAP. 



(1900), and others. Oerum experimented for thirty-three successive 

 days on a dog, alternating days of fasting with days on which he gave 

 meat or gelatine. When he gave meat there was a gain in the 

 balance of nitrogen ; when he gave gelatine there was a deficit. 

 This result is clearly shown by the following table : 



The hydrolytic decomposition of gelatine into its component 

 groups proves it to be lacking in cystine, tyrosin, and tryptophane. 

 Kauffmann considers the inability of gelatine, and, in general, of 

 the group of albuminoids properly so-called, to take the place of 

 protein to be due to this defective chemical constitution. He 

 experimented on himself and found it possible to preserve nitro- 

 genous equilibrium if he substituted a mixture of gelatine, tyrosin, 

 tryptophane, and cystine for the nutritive proteins. This result 

 has however been contradicted by Bona and W. Miiller, who 

 found that the addition of tyrosin and tryptophane to gelatine 

 did not effect any economy in the consumption of nitrogen. 

 Further and more numerous researches are necessary before this 

 question can be regarded as definitely settled. 



(c) We know that during digestion in the stomach and 

 intestines the neutral fats are resolved into free fatty acids and 

 glycerine (Vol. II. Chapters III. and IV.). The nutritive value 

 of neutral fats is the same as that of the fatty acids contained in 

 them. This has been proved by numerous researches. I. Munk, 

 for instance, obtained nitrogenous equilibrium in a dog by giving 

 it 800 grins, of meat and 70 grms. of fat. The equilibrium 

 remained unchanged when he substituted for the 70 grms. of 

 fat the fatty acids extracted from that quantity of fat. He 

 therefore concluded that fatty acids effect the same economy in 

 the consumption of protein as the corresponding quantity of 

 neutral fats would do. This fact will be easily understood if 

 we reflect that fat contains only about 9 per cent of glycerine 

 and that the heat of combustion of glycerine is about half that 

 of fat. The substitution of the corresponding fatty acids for 

 nutritive fats does not therefore produce a noticeably different 

 effect on the organism. 



If, on the other hand, a large quantity of glycerine (40-70 



