430 CHEMISTR Y OF THE DIGESTIVE PROCESSES. 



chloride, while deuterogelatose is only precipitated by saturation with 

 ammonium sulphate. Protogelatose is also precipitated by platinic 

 chloride, while deuterogelatose is not so precipitated. 



Collagen is not attacked by pancreatic juice unless it has been 

 previously boiled with water, or swollen by the action of dilute acids, as 

 it normally would be by the gastric juice. 1 This result is confirmed by 

 the observation of Ludwig and Ogata, that after removal of the stomach 

 proteid was still digested, but connective tissue was not attacked. After 

 such preliminary treatment collagen is easily converted into gelatin, 

 and the after course of events closely resembles that described for 

 peptic digestion. There is first formed protogelatose, then deutero- 

 gelatose, and finally gelatin peptone, which is not converted by any 

 further action of trypsin into amido-acids. 2 Trypsin acts so easily on 

 gelatin, and deprives it so readily of its power of gelatinising, that this 

 has been recommended by Fermi as a test for trypsin. 3 



The decomposition products of gelatin have been long known, though not 

 with the exactitude above described. Gmelin showed that it was decom- 

 posed by superheated steam at 140 C., and Hofmeister 4 obtained, after boil- 

 ing with water in 1 per cent, solution for thirty hours, two cleavage products 

 which he termed semiglutin and semicollin ; these are probably identical with 

 proto- and deuterogelatose. 



Elastin is also dissolved by pepsin and hydrochloric acid, 5 though 

 with more difficulty than collagen. The products of the peptic digestion 

 of elastin were studied by Horbaczewski, 6 who described two products 

 which he called hemielastin and elastin peptone. The same subject has 

 been investigated more recently by Chittenden and Hart, 7 who have 

 shown that two substances are formed in the peptic digestion of elastin, 

 but that both these substances are albumoses, since they are both pre- 

 cipitated by saturation of their solutions with ammonium sulphate ; to 

 these substances they gave the names of protoelastose and deutero- 

 elastose. The former is precipitated on saturation of its solution with 

 sodium chloride, while the latter is only precipitated on the addition of 

 acetic acid. Elastin is also directly attacked by trypsin and dissolved, 

 forming in turn proto- and deuteroelastoses as in peptic digestion, but 

 neither in peptic or tryptic digestion is there any peptone formed. 8 



1 Ewald and Kiihne, Verhandl. d. naturh.-med. Ver. zu Heidelberg, 1877, N. F., 

 Bd. i. S. 451. 



2 Chittenden and Solley, loc. cit. 



3 Arch. f. Hyg., Miinchen u. Leipzig, 1891, Bd. xii. 



4 Ztschr. f. physiol. Of/em., Strassburg, 1878, Bd. ii. S. 299. 



5 Etzinger, Ztschr. f. BioL, Miinchen, Bd. x. S. 84. 



6 Ztschr. f. physiol. Chem., Strassburg, 1882, Bd. vi. S. 330. 



7 Ztschr. /. BioL, Miinchen, 1889, Bd. xv. S. 368. 



8 Chittenden and Hart, loc. cit. 



