ALBUMINS OR PROTEINS. 205 



only slightly attacked by the pepsin, remains undissolved for the most 

 part, and for this reason was first discovered. 



The pepsin of the gastric juice also possesses another action besides 

 that of direct disintegration. It causes milk to curdle. This striking 

 property, not yet entirely explained, is due to a specific ferment, known 

 as rennin, 1 or chymosin. We will state at once that the assumption of a 

 separate ferment has been questioned. Pawlow and Parastschuk 2 con- 

 clude, from their experiments, that the two actions attributed usually 

 to pepsin and rennin are due to the same ferment. They arrive at this 

 conclusion from the fact that the proteolytic- and milk-coagulating effects 

 of the gastric juice take place parallel to one another. Both actions are 

 accelerated and retarded by the same influences, not only qualitatively, 

 but also quantitatively. We know that neither the pepsin nor the rennin 

 is secreted as such in the walls of, the stomach. Both are found in the 

 inactive form as zymogen. It is only by the action of acid that this zymogen 

 is converted into active ferment. Activating these ferments of the gastric 

 juice is another important function of its acid contents. The ferments are 

 only present in their inactive state, and are incapable of doing their work 

 when the free acid of the gastric juice is missing. Pepsin and rennin are 

 both rendered active by the same agent; in fact, to the same extent. 

 This parallelism has caused the Russian authors above mentioned to 

 stop speaking of two ferments, but of two different actions of one and 

 the same ferment. We cannot, at this time, accept Pawlow's decision. 

 The more we study the action of ferments, the clearer it becomes that they 

 are delicately adjusted for definite compounds, and are influenced by 

 very slight differences of configuration. In fact, such differences in the 

 configuration of molecules are oftentimes first indicated by the fact that 

 a ferment does or does not act upon a certain substance, whereas its 

 ordinary chemical behavior has not led us to suspect such a difference. 

 This of itself is sufficient to make it seem improbable that a ferment 

 could have two such different actions. An important objection immedi- 

 ately arises. We do not exactly know how to interpret the activity of 

 rennin. It is, of course, possible that this activity may produce the same 

 result as does pepsin, namely, an hydrolysis. We know that the essential 

 function of rennin consists, not, as formerly believed, in the curdling of the 

 casein, but in the conversion of casein into another albuminous body, 

 possessing entirely different characteristics. If the assumption be correct 

 that this is merely a hydrolysis, then the analogy to that of pepsin would 

 be complete. We would only have to assume that the nature of the 



1 Cf. O. Hammarsten: Sitzber. kgl. Gesellsch. Wissensch. Upsala, 1877. 



2 Z. physiol. Chem. 42, 415 (1904), and Die Identitat des Pepsins und Chymosins. 

 Verhandl. Sektion Anat., Physiol. mediz. Chem. Vers. nordischer Naturforscher u. Aerzte 

 in Helsingfors. 7, 12, July, 1902, p. 28. 



