168 LECTURE VIII. 



by erepsin. The decomposition products are the same as those produced 

 by trypsin. At present it is difficult to pass judgment on the actual 

 existence of this ferment. According to the investigations of Vernon, 1 

 it occurs widely distributed in the animal kingdom, and is to be found in 

 all tissues. It is very difficult to decide whether the proteolytic ferments 

 should be considered as homogeneous or as mixtures of ferments of differ- 

 ent individual functions. It is not unreasonable 2 to assume that for each 

 protein, or for a class of these substances, a special series of ferments exists. 

 On the other hand, we could easily imagine that one ferment follows 

 another, step by step, in the decomposition, in the same manner as is 

 true with the carbohydrates, in which case diastase decomposes them 

 only to the maltose stage, leaving the latter to be further acted upon by 

 maltase. 3 



As a matter of course, proteolytic ferments must also be active in the 

 tissues and cells, and many observations indicate that the action is anal- 

 ogous to that of trypsin. This applies not only to the animal cells, but 

 also to those of plants. Especially noteworthy is the ferment papayotin 

 occurring in the milk of the melon, Carica papaya. It quickly dissolves 

 albumin. Its action appears to be similar to that of trypsin. 4 Other 

 active ferments have also been isolated from various plants, as, for instance, 

 from the sap of the fig-tree, Ficus carica, and macrocarpa. Other plants, 

 like the banana, are credited with possessing a ferment analogous to 

 pepsin. 



Especial interest attaches to those plants which also secrete ferments 

 externally which correspond to the digestive fluids characteristic of the 

 animal organism. They constitute the large group of carnivorous plants. 

 We will mention merely the Drosera and Pinguicula, growing in peat 

 bogs; and the varieties of Utricularia inhabiting brooks and stagnant 

 pools. The Nepente species, Dioncea muscipula, act on a larger scale. It 

 is still a question whether the action of the ferment produced is analogous 

 to that of pepsin or to that of trypsin. It has even been suggested that the 

 fermentative action of Nepente is due to bacteria. 



In the cryptogams the proteolytic ferments are also widely distributed, 

 and in many cases have been detected. 



Before discussing the manner in which the fundamental constituents of 

 the albumins are combined, we must devote a little attention to several 

 other substances which occur among the cleavage-products of the proteins, 



1 H. M. Vernon: J. Physiol. 32, 33 (1904); 33, 81 (1905). 



2 Cf . Lecture on Ferments. 



8 Cf. W. M. Bayliss and E. H. Starling: J. Physiol. 29, 174 (1903). K. Mays: Z. 

 physiol. Chem. 38, 428 (1903). L. Pollak: Hofmeister's Beitr. 6, 95 (1904). K. Kiesel: 

 Pfliiger's Arch. 108, 334 (1905). 



4 O. Emmerling: Ber. 36, 695 (1902). 



