CHEMISTRY OF DIGESTION AND NUTRITION. 



233 



therefore be distinguished or separated from the so-called " true peptones." We 

 must await further investigations before attempting to come to any conclusion 

 upon this point. It is well to bear in mind that the change from ordinary 

 proteid to peptone evidently takes place through a number of intermediate steps, 

 and the word peptone is meant to designate the final product. Whether this 

 final product is a chemical individual with properties separating it from all the 

 intermediate stages is perhaps not yet fully known, but, provisionally at least, we 

 may adopt Kiihne's definition, outlined above, of what constitutes peptone, as it 

 seems to be generally accepted in current literature. Peptones are characterized 

 by their diffusibility, and this property is also possessed, although to a less 

 marked extent, by the proteoses. Recent work by Chittenden, 1 in which he 

 corroborates results published simultaneously by Kiihne, shows the following 

 relative diifusibility of peptones and proteoses. The solutions used were approx- 

 imately 1 per cent. ; they were dialyzed in parchment tubes against running 

 water for from six to eight hours, and the loss of substance was determined 

 and expressed in 'percentages of the original amount. Proto-proteose gave a 

 loss of 5.09 per cent.; deutero-proteose, 2.21 percent.; peptone, 11 percent. 

 Several elementary analyses of proteoses and peptones have been reported, 

 but they cannot be accepted as final, owing to the fact that the substances 

 analyzed were probably mixtures, and not chemical individuals. The follow- 

 ing analyses, reported by Chittenden, 2 will serve to show the relative percentage 

 composition of these bodies : 



Phyto-vitellin, a Crystallized Proteid extracted from Hemp-seed. 



The most striking differences in composition observed in passing from the 

 mother-proteid to the peptones are the progressive decrease in the percentage 

 of carbon and the increase in the percentage of oxygen. Both these facts are 

 in accord with the general theory that proteolysis consists essentially in a series 

 of hydrolytic cleavages. 



Rennin. In addition to pepsin the gastric secretion contains an enzyme 

 which is characterized by its coagulating action upon milk. It has long been 

 known that milk is curdled by coming into contact with the mucous membrane 

 of the stomach. Dried mucous membrane of the calf's stomach, when stirred 

 in with fresh milk, will curdle the latter with astonishing rapidity, and this 

 property has been utilized in the manufacture of cheese. Hammarsten discovered 

 that this action is due to the presence of a specific enzyme which exists ready 

 formed in the membrane of the sucking-calf's stomach, and which is present 



1 Journal of Physiology, vol. xiv., 1893, p. 502. 



2 Cartwright Lectures, New York Medical Record, April, 1894. 



