DIGESTION OF BODIES ALLIED TO PROTEIDS. 429 



acids and proteid, and the nucleic acids in their turn into nuclein bases 

 and phosphoric acid. These changes take place very slowly in tryptic 

 digestion. On digestion with pepsin and hydrochloric acid, the glyco- 

 proteids are 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 1 found that 

 it contained inorganic phosphorus, and that it is a mixture of which one part is 

 soluble in dilute sodic carbonate (Na 2 C0 3 ), 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 2 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 O13 

 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, yielding 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. Untersuch., Berlin, 1871, S. 463. 



2 Stud. Lab. Physiol. Chem., New Haven, 1890, vol. iii. p. 66. 



3 Inaug. Diss., Bern, 1893. 



4 Centralbl.f. d. med. Wissensch., Berlin, 1893, Nos, 23, 28; Arch. f. d. ges. Physiol. , 

 Bonn, 1896, Bd. Ixiii. S. 401. 



3 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. 



