i EXCHANGE OF MATEEIAL 35 



addition to the gelatine. Gelatine therefore is not only useless, 

 but harmful, since it disturbs the digestion. 



Frerichs and Mulder (1843) called in question the experi- 

 ments made by the French commission and Magendie, and 

 proved that gelatine cannot be substituted for protein, bufc that 

 it economises the consumption of protein just as do sugar and 

 fats. 



In order to decide the matter, the balance of nitrogen in the 

 dogs under experiment had to be ascertained ; this was first done 

 by Bischoff and Voit in 1860. They found that the whole of the 

 nitrogen contained in the gelatine taken was eliminated in the 

 urine. Gelatine, therefore, decomposes readily, and on the same 

 day. Even when large quantities of it are given, the quantity of 

 nitrogen in the urine is always larger than that in the gelatine 

 taken, hence it cannot be regarded as a substitute for genuine 

 albumens. If it be added to a diet of meat, it economises its 

 consumption to a greater degree than fats and saccharides will do. 

 It cannot be built up, but it burns readily, better than fats and 

 sugars. 



If animals be fed on raw collagenous tissues, bones, cartilages, 

 tendons, connective tissues, it will be found that, while most of 

 these substances are digested, they cannot take the place of 

 protein substances properly so-called, although they economise 

 the consumption of such substances. Hence the inability of 

 gelatine to act as a building-up food is due to its molecular con- 

 stitution and not to the chemical change undergone by the 

 nitrogenous components of the tissues from which it is extracted 

 during the process of boiling. 



Voit and Pettenkofer (1872) considered that gelatine may also 

 effect an economy in the consumption of the fat of the body, 

 though to a smaller extent than saccharides and fats taken in 

 food. The addition of gelatine to a lavish diet of meat causes an 

 increase not only in flesh but also in the deposit of fat. The 

 above-mentioned authors think, however, that this increase in fat 

 is due to formation from proteins, not from the gelatine taken. 



The decomposition of the gelatine eaten is brought about by 

 the tissues, probably by the enzymes which they contain or produce 

 during their metabolic activity. During my experiments on long 

 fasts, both in Succi and in dogs, I found that gelatine decomposed 

 slowly in four to five days and not on the same day, possibly 

 because the enzymes decreased as the result of inanition. This 

 decrease in the enzymes would also explain the fact that during 

 inanition the discharge of nitrogen gradually decreases, i.e. the 

 consumption of the albumens contained in the organs is economised. 



Voit's researches into the nutritive value of gelatine were 

 confirmed in all essential points by those made more recently by 

 Oerum (1879), Pollitzer (1885), I. Munk (1894), and Kirchmann 



