18 GASTRIC DIGESTION OF PROTEINS 



tions of Lang and Tobler, as well as his own, upon horses 

 and dogs). 



Comparative Physiological Considerations. Our view 

 of physiological processes of any sort is bound to be un- 

 duly warped and limited if we confine ourselves to 

 human beings and the ordinary laboratory experiment ani- 

 mals. Nothing less than a consideration of all classes of 

 life forms can assure a thoroughly scientific basis. William 

 Biedermann 49 by the monumental work in which he has 

 collected and critically dealt with the whole mass of material 

 bearing on digestion from the standpoint of comparative 

 physiology, has certainly earned a claim to general gratitude 

 from all who are concerned with biological studies. The 

 author feels that at least a few brief considerations should 

 be given to this side of the subject, restricting himself, how- 

 ever, to the vertebrates because he has elsewhere dealt with 

 the chemistry of digestion in invertebrates. 50 



In the first place, among fishes 51 there occur forms with- 

 out stomachs (among others, amphioxus, the cyclostomata 

 and cyprinoids). In the cyprinoid fishes the opening of the 

 gall duct lies just back of the cesophageal opening into the 

 intestine; and, of course, it is impossible that in such case 

 there could be the least trace of gastric digestion in its 

 ordinary meaning. Most fishes, however, possess a stom- 

 ach, the glands of which secrete an enzyme capable of digest- 

 ing protein substance in an acid reaction. The most exact 

 work in this connection has been done upon the selachians. 

 There is divergence of opinion as to the existence of free 

 hydrochloric acid in the gastric juice of sharks (recently 



4 W. Biedermann, Handb. d. vergl. Physiol., H. Winterstein, 2' (Die 

 Aufnahme, Verarbeitung und Assimilation der Nahrung, pp. 1563, Jena, 1911). 



80 O. v. Fiirth, Vergleichende chemische Physiologic der niederen Tiere, 

 pp. 140-330, Jena, 1903. 



n Literature upon gastric digestion in fish: A. Scheunert, Handb. d. 

 Biochem., 3", 163-167, 1909; W. Biedermann, 1. c., pp. 1088-1106; cf. also 

 D. D. Van Slyke and G. F. White, Journ. of Biol. Chem., 9, 209, 1911. 



