43o 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 Hof meister 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 Kuhne, Verhandl. d. natwrh.-med. Vcr. zu Heidelberg, 1877, N. F., 
Bd. i. S. 451. 
2 Chittenden and Solley, loc. cit. 
3 Arch. f. Hyg., Miinehen u. Leipzig, 1891, Bd. xii. 
4 Ztschr. f.physiol. Clicm., Strassbwg, 1878, Bd. ii. S. 299. 
5 Etzinger, Ztschr. f. Biol., Miinehen, Bd. x. S. S4. 
6 Ztschr. f.physiol. Ckem., Strassbnrg, 1SS2, Bd. vi. S. 330. 
7 Ztschr. f. Biol., Miinehen, 1S89, Bd. xv. S. 368. 
8 Chittenden and Hart, loc. cit. 
