82 GELATIN. 



formed to which the name gelatoses or glutoses may be applied and 

 which have so far been distinguished as proto- and deutero-gelatose. 

 Accompanying these, in variable amount, are other products known 

 as gelatin-peptones. The latter are to be regarded as a product of 

 the further action of the enzymes on the first formed gelatoses and, 

 like the true peptones in their relationship to the albumoses, may be 

 separated from them by their non-precipitability on saturation with 

 ammonium sulphate, a reagent which completely precipitates the 

 gelatoses. Protogelatose is partially precipitated by saturation of 

 its solution with common salt, and completely so on the simultaneous 

 addition of acetic acid. Deuterogelatose is not precipitated by either 

 of the above reagents 1 . The so-called true gelatin-peptones have not 

 yet been obtained in sufficient quantity to admit of their complete 

 examination. The products of the digestion of gelatin appear to give 

 a distinct biuret reaction with caustic soda and sulphate of copper, 

 and like the peptones (and albumoses) are not precipitated by tauro- 

 cholic acid, which precipitates gelatin from its solutions 2 . 



When the spores of Penicillium are sown on a surface of gelatin, as soon as the 

 mycelium is well developed the subjacent gelatin liquefies sometimes to a con- 

 siderable depth, so that the Penicillium finally floats on a layer of fluid separated 

 by some distance from the remaining still solid gelatin. The fluid in this layer 

 now yields an intense biuret reaction. A similar liquefaction is observed during 

 the growth of certain bacteria and other micro-organisms on gelatin. 



The fact has already been referred to ( 524) that gelatin taken as food, while 

 it materially lessens both the nitrogenous, and to some slight extent the non- 

 nitrogenous metabolism of the body, and thus appears able to undergo a destructive 

 metabolism similar to that of the proteids, cannot, on the other hand, play any 

 part in the constructive nitrogenous metabolism which leads to the formation of 

 proteids. In other words the nitrogen contained in gelatin cannot be built up 

 into the nitrogen of a proteid 3 . We do not as yet possess any information which 

 enables us to formulate any reason for this special behaviour of gelatin. It has 

 been suggested that the absence of aromatic residues in gelatin (see above) might 

 account for the phenomenon 4 , but experiments in which animals have been fed 

 with gelatin + tyrosin have not confirmed this view 5 . It appears that a considerable 

 amount of gelatin is digested and absorbed in man, since none appears in the 

 faeces, and meat (muscle) may contain as much as 2 p.c. of gelatin : further, Voit's 

 experiments show that a dog may digest and absorb 50 p.c. of the gelatin 

 administered in the form of bones 6 . Bearing these facts in mind and knowing 



1 Chittenden and Solley, JL of Physiol. Vol. xn. (1891), p. 23. See also Klug, 

 Pfliiger's Arch. Bd. XLVIII. (1890), S. 100. The latter author describes further a 

 product to which he gives the name apoglutin. It makes its appearance as an 

 insoluble substance, hence resembling antialbumid or dyspeptone, during the 

 digestion of gelatin. 



2 Emich, Monatshefte f. Chem. Bd. vi. (1885), S. 95. 



3 Voit, Zt.f. BioL Bd. vm. (1872), S. 297; x. (1874), S. 203. 



4 Hermann u. Escher, Vierteljahrsch. d. natforsch. Gesell. in Zurich, 1876, S. 36. 



5 Lehmann, Sitzber. d. Gesell. f. Morphol. u. Physiol. Miinchen, 1885. 



6 See also Etzinger, Zt.f. BioL Bd. x. (1874), S. 84. 



