CHEMICAL BASIS OF THE ANIMAL BODY. 81 



and potassium in acid solution. Several acids on the other hand 

 precipitate it readily, such as phosphotungstic and metaphosphoric, also 

 taurocholic and tannic. Of the two last-named acids the former 

 yields an opalescence in presence of 1 part of gelatin in 300,000 of 

 solution, and the latter in still more dilute solutions 1 . The precipita- 

 bility with tannic acid seems to depend on the presence of neutral 

 salts 2 . The specific rotatory power of gelatin in aqueous solution or in 

 presence of a trace of alkali is stated to be (a) D - 130 at 30 C. 

 and to be reduced to -112 or 114 on the addition of more alkali 

 or acetic acid 3 . This statement requires confirming. 



When decomposed in sealed tubes with caustic-baryta gelatin yields 

 on the whole the same products as do the proteids 4 , with the exception 

 of tyrosin ; neither this nor any other substance of the typically 

 aromatic series, is ever obtained during any decomposition of gelatin 

 whether by chemical or putrefactive processes 5 . By prolonged boiling 

 with hydrochloric acid it yields glycin (glycocoll), leucin, glutarnic acid 

 and ammonia 6 , and with sulphuric acid aspartic acid as well 7 . 



Gelatin-peptones 8 . By prolonged boiling with water (1 p.c. solution 

 boiled for 30 hours), or shorter treatment in a Papin's digester, also by 

 heating with hydrochloric acid (4 p.c. at 40), or still more readily 

 by pepsin in presence of acid or by trypsin 9 , 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 10 . From the conditions under which the change is effected and 

 from certain evidence 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. 



Recent researches have shown that, the hydrolytic decomposition 

 of gelatin by digestive enzymes .gives rise to products analogous to 

 those obtainable by the same method from the proteids. Thus during 

 both its peptic and tryptic digestion certain primary products are 



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



2 Weiske, loc. cit. 



3 J. de Bary, Diss. Tubingen, 1864. Also in Hoppe-Seyler's med.-chem. Unters. 

 Hft. 1, 1866, S. 73. 



4 Schiitzenberger et Bourgeois, Gompt. Eend. T. LXXXII. (1876), p. 262. 



5 Nencki. See Abst. in Maly's Bericht. 1876, S. 31. Jeanneret, Jn. f. prakt. 

 Chem. (N.F.) Bd. xv. (1877), S. 353. Weyl, Zt. f. physiol. Chem. Bd. i. (1877), S. 

 339. 



6 Horbaczewski, Sitzb. d. Wien. Akad. Bd. LXXX. (1879), 2 Abth. Juni.-Hft. 



7 Gaehtgens, Zt. f. physiol. Chem. Bd. i. (1877), S. 299. 



8 Hofmeister, Zt. f. physiol. Chem. Bd. n. (1878), S. 299. Gives literature down 

 to that date. Tatarinoff, Compt. Rend. T. xcvn. (1883), p. 713. 



9 Schweder, Inaug.-Diss. Berlin, 1867. 



10 Uffelmann, Arch. f. klin. Med. Bd. xx. (1877), S. 535. 



