82 GELATIN. 



ter, also by heating with hydrochloric acid (4 p.c. at 40), or still 

 more readily by pepsin in presence of acid or by trypsin, 1 gelatin 

 loses its power of solidifying on cooling, and is converted into 

 more highly soluble and now diffusible substances, to which the 

 name of gelatin-peptones has been given. A similar change 

 occurs when gelatin is taken into the stomach. 2 From the con- 

 ditions under which the change is effected and from certain evi- 

 dence deducible from analysis there can be but little doubt that 

 the conversion takes place as the result of hydrolysis, as in the 

 case of the formation of true peptones from proteids. 



Eecent researches have shown that the hydrolytic decomposi- 

 tion of gelatin by digestive enzymes gives rise to products analo- 

 gous to those obtainable by the same method from the proteids. 

 Thus during both its peptic and tryptic digestion certain primary 

 products are 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 relation- 

 ship 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. 3 The so-called true gelatin-peptones have not yet been 

 obtained in sufficient quantity to admit of their complete exami- 

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

 a distinct biuret reaction with caustic soda and sulphate of cop- 

 per, and like the peptones (and albumoses) are not precipitated 

 by taurocholic acid, which precipitates gelatin from its solutions. 4 



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 considerable depth, so that the Penicillium finally 

 floats on a layer of fluid separated, by some distance from the re- 

 maining 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 



1 Schweder, Inauq.-Diss. Berlin, 1867. 



2 Uffelmann, Arch. f. kUn. Med. Bd. xx. (1877), S. 535. 



3 Chittenden and Solley, .//. of Physiol. Vol. xii. (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 diges- 

 tion of gelatin. 



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



