FOOD AND DIGESTION 351 



there is a continuance of the conversion of starch to sugar 

 which was started in the mouth, and at the same time the 

 micro-organisms go on splitting the sugar to form lactic acid, 

 which may thus be regarded as a normal constituent of the 

 stomach during the first half-hour after a mixed meal. In 

 the dog ptyalin is absent. 



(2) Proteolytie Period. Before the amylolytic period is com- 

 pleted, the gastric juice has begun its special action on proteins. 

 This may be readily studied by placing some coagulated protein 

 in gastric juice, or in an extract of the mucous membrane of 

 the stomach made with dilute hydrochloric acid, and keeping 

 it at the temperature of the body. The protein swells, becomes 

 transparent, and dissolves. The solution is coagulated on 

 boiling a soluble native protein has been formed. Very soon 

 it is found that, if the soluble native protein is filtered off, the 

 filtrate gives a precipitate on neutralising, showing that an acid 

 proteate (meta-protein) has been produced. If the action is 

 allowed to continue and the acid proteate precipitated and 

 filtered off, it will be found that the filtrate gives a precipitate 

 on saturating with common salt, showing that a proto-proteose 

 has been formed. Along with this a certain amount of hetero- 

 proteose is also formed. It is characterised by being precipitated 

 on neutralisation and by being insoluble in distilled water. On 

 filtering off' these, the filtrate yields a precipitate on saturating 

 with ammonium sulphate, indicating the formation of a deutero- 

 proteose, and, if the filtrate from this be tested, the presence of 

 a protein may be demonstrated. Peptone has been produced. 

 (Chemical Physiology.) 



These changes may be represented in the following table : 



Coagulated Protein. 



Soluble Native Protein. 



Acid Proteate (Meta-protein). 



Proto-proteose. Hetero-proteose. 



I I 



Deutero-proteose. Deutero-proteose. 



Peptone. Peptone. 



