46 MEAT EXTEACTS. 



higher degree than either fat or carbohydrates. It can be shown that large quantities 

 of gelatin spare more proteid from combustion than do small quantities; that, however, 

 proteid is lost from the body even' if with large quantities of gelatin the greatest possible 

 amount of fat be given. A direct laying-on of gelatin, either in the glutin-yielding 

 tissues or in the proteid-forming tissues, is not possible, and it must therefore be 

 assumed that when gelatin is formed in the body it is at the expense of proteid. Gela- 

 tin, for this reason, is capable of replacing proteids of the food only in part. " 



Voit made no special attempt to set the limits within which proteid 

 may be so replaced, but gives for a large dog these figures: 168 grams 

 of dry gelatin spared 84 grams of dry flesh. 6 



The next investigation bearing on the comparative value of gelatin 

 and proteid was that of Oerum, c who placed a dog on a daily diet of 

 meat, starch, butter, and meat extracts; he then replaced all of the 

 meat with enough gelatin to maintain the same nitrogen supply. He 

 records a considerable increase in the nitrogen of the urine in the 

 latter case. 



Pollitzer, d in the course of some experiments undertaken to prove 

 that the products of proteid digestion are to be classed with the pro- 

 teids themselves, and not with the proteid-sparing foods merely, 

 compared the effects of gelatin on the nitrogen output with those of 

 horseflesh and its products of gastric digestion. He concludes that 

 peptone and hemialbumose (prepared by Kuhne's methods) have a 

 nutritive value which is in "sharp contrast with the considerable loss 

 of nitrogen which takes place after feeding an equivalent amount of 

 gelatin." 



Ganz e fed PaaFs glutin-peptone and was able to cover more than 

 half of the total nitrogen requirements therewith. Gerlach f also pre- 

 pared a "glutin-peptone," and found that it is a good "sparing agent," 

 but is not of itself able to replace proteid. 



Munk a in a brief series of experiments attempted to find the "upper 

 limit for the substitution of food proteid with gelatin," and reached 

 the conclusion that at least half as much proteid must be fed as is 

 destroyed by the animal in fasting, if nitrogen equilibrium is to be 

 maintained. 



Kirchmann, A in a very painstaking research with proteid-free 

 gelatin, determined that the proteid destruction may be reduced 

 under the influence of gelatin alone as much as 35 per cent, and that 

 this maximum effect is obtained when 62 per cent of the body's 

 energy requirement is supplied by the gelatin. 



"Zts. Biol., 1872, 5:297. 

 b Ibid. 



cXordiskt medicinskt Arkiv, 1879, vol. 11, reviewed by Hammarsten in Maly'fl 

 Jahresbericht fur Thierchemie, 1879, 9: 308. 

 d Archiv gesam. Physiol., 1885, 37 : 301. 

 « Quoted by Kirchmann, Zts. Biol., 1900, 40:54. 

 / Die Peptone. Hamburg and Leipzig, 1891. 

 9 Archiv gesam. Physiol., 1894, 58 : 309. 

 h Loc. cit. 



