208 LECTURE X. 



plained. If some rennin is added to a clear solution of the so-called albu- 

 moses and peptones, a flocculent precipitate is formed. This is called 

 plastein, and is supposed to occur only in the presence of albumoses. 

 Its amount has been variously estimated, from 3 to 27 per cent. It is 

 suggested that the closer the cleavage-products stand in relation to albu- 

 min, the more readily will they be precipitated by rennin. The forma- 

 tion of plastein is still unexplained. It has been looked upon as a 

 synthetic process, although this assumption has not been substantiated by 

 any experimental proof. 1 



The albumin, already partly disintegrated, passes from the stomach 

 into the duodenum, being there subjected to the influence of the pancreatic 

 juice, and especially to the trypsin contained therein. This also is not 

 delivered to the intestines, as such. It is secreted in the zymogen form, 

 and only becomes active in the intestine. There is a substance, called 

 " enterokinase," in the intestinal juice, which converts the trypsin- 

 zymogen into the active ferment. We shall return to this particular 

 process later. We were a long time uncertain regarding the extent of 

 the decomposition of the albumins reaching the duodenum in the form of 

 a mixture of peptones of different degrees of complexity. We assumed, 

 until recently, that, as a rule, only the so-called albumoses and peptones 

 were formed, and that these were absorbed directly. Such a conception is 

 particularly plausible, if, as has been generally done, digestion is only 

 regarded as a means of preparing the nutrient material for absorption. 

 This assumption was still believed, even when free amino acids, especially 

 leucine and tyrosine, were repeatedly found in the alimentary canal. This 

 view obtained added support from the experiment of Hof meister. 2 He put 

 a piece of the stomach or intestinal wall of a recently killed animal in a 

 moist chamber for a time at 40 C., and showed that its peptone content 

 had diminished when compared with a piece of the same size, whose 

 peptone content had been immediately estimated. In fact, after two 

 to three hours, all the peptones had disappeared. Salvioli 3 also showed 

 that peptones quickly disappeared when introduced into a ligated intes- 

 tine. There seems to be no doubt that peptones are absorbed; in fact, 

 it has even been asserted that albumin itself is directly taken up. It 

 was shown by the researches of Kutscher and Seeman, 4 and of O. 



1 Cf. A. Danilewsky and Okunew: Inaug. Diss. St. Petersburg, 1895. M. Lawrow: 

 Inaug. Diss. St. Petersburg, 1897. Sawjalow: Diss. Jurjew. 1899, and Pfliiger's Arch. 

 86, 171 (1901). H. Bayer: Hofmeister's Beitrage, 4, 554 (1903). M. Lawrow and S. 

 Salaskin: Z. physiol. Chem. 36, 277 (1902). Kurajeff: Hofmeister's Beitrage, 1, 121 

 (1901); 2, 141 (1902). 



2 Pfltiger's Arch. 19, 8 (1885). 



8 Arch. Anat. Physiol. Sup. 1880, p. 95. 



Z. physiol. Chem. 34, 528 (1901 and 1902); 35, 432 (1902). 



