DIGESTION OF BODIES AILIED TO PROTEIDS. 429 
acids and proteid, and the nucleic acids in their turn into nuclein bases 
and phosphoric acid. Those changes take place very slowly in tryptic 
digestion. On digestion with pepsin and hydrochloric acid, the glyco- 
proteins arc decomposed, yielding a carbohydrate substance which 
reduces Fehling's solution and a proteid which as before is peptonised. 
This decomposition only takes place slowly, and is probably due in 
great part to the feeble hydrolytic action of the hydrochloric acid. 
The caseinogen of milk is first coagulated by the action of the rennin 
of the gastric juice, and afterwards the insoluble casein formed in this 
process is digested. 
Casein is broken up in the process of gastric digestion into a proteid 
and pseudo-nuclein, of which the former is changed into peptone, while 
the latter is thrown out as an insoluble precipitate. 
This precipitate corresponds to the dyspeptone of Meissner, and has been 
the subject of a considerable amount of investigation. Lubavin l found that 
it contained inorganic phosphorus, and that it is a mixture of which one part is 
soluble in dilute sodic carbonate (XaoCCX), while the other is insoluble. The 
soluble part contains 4 - 6 per cent, of phosphorus, and is probably identical 
with Hoppe-Seyler's nuclein. Chittenden - and others state that dyspeptone does 
not contain much phosphorus, and that this is probably present as calcium 
phosphate, dyspeptone being therefore not a nuclein but a mixture of calcium 
phosphate with a hydration product of casein. C. Wildenow 3 does not hold 
with this view, having obtained dyspeptone which contained only 0T3 
per cent, of calcium, and 3 - 85-4"66 per cent, of phosphorus, but agrees with 
Lubavin that the precipitate is a nuclein. E. Salkowski 4 supports this con- 
clusion ; he also announces that on prolonged digestion the precipitate 
redissolves to a clear solution, part of the phosphorus being split off as 
phosphoric acid, and part remaining in organic combination (probably as 
paranucleic acid). Such a solution can be brought about, according to 
Salkowski, by a strong peptic solution within forty-eight hours. 
The albuminoids as a class are fairly resistant to the action of 
digestive agents ; when they are broken up, they yield products closely 
resembling those furnished by the decomposition of the true proteids. 
Collagen is said to be converted into its hydrate gelatin more 
rapidly by the action of pepsin and hydrochloric acid than it would be 
by the acid alone ; the gelatin thus formed is then acted upon by the 
pepsin and hydrochloric acid, and rapidly loses its characteristic property 
of gelatinising on cooling. 5 This physical change is the visible sign of a 
chemical one, by which the gelatin is converted into a substance called 
protogelatose ; this is again changed, wielding deuterogelatose ; and finally 
gelatin peptone is formed. 6 These substances resemble the corresponding 
compounds of proteid digestion, the gelatin peptone being distinguished 
from the other two products by its indifference to the saturation of its 
solutions with neutral salts and by its diffusibility. Protogelatose is 
thrown out of solution by saturation of its acidified solution with sodium 
1 Med.-chem. Uviersuch., Berlin, 1871, S. 463. 
2 Stud. Lab. Physiol. Chem., New Haven, 1890, vol. iii. p. 66. 
3 Inaug. Diss., Bern. 1893. 
4 Ccntralbl. f. d. meal. TVissensch., Berlin, 1893, Nos, 23, 28; Arch. f. d. ges. Physiol., 
Bonn, 1896, Bd. lxiii. S. 401. 
5 J. de Bary, Ztschr. f. physiol. Chem., Strassburg. 1896, S. 75 ; Etzinger, Ztschr. f. 
Biol., Miinchen, Bd. x. S. 84 ; Uffelmann, Deutsches Arch. f. klin. Med., Leipzig, Bd. xx. 
S. 535. 
6 Chittenden and Solley, Journ. Physiol., Cambridge and London, 1891, vol. xii. p. 23. 
