152 MANUAL OF PHYSIOLOGY. 



All these requisites are found in the normal act of digestion. 

 The temperature of the stomach is 38 to 39 C. (=100F.). 

 Hydrochloric acid is present in the proportion of about .2 per cent. : 

 as quickly as the peptones are formed they can be removed by 

 absorption from the stomach, and thus the needful dilution is ac- 

 complished : and finally, if the mouth has done its duty, the pieces 

 of proteid have been reduced to a pulp, composed of minute par- 

 ticles: these are kept in constant motion by the gastric walls, and 

 thus are repeatedly brought in contact with fresh supplies of the 

 digestive fluid. 



There can be little doubt that the conversion of proteid into 

 peptone is normally brought about by the pepsin, which acts as a 

 ferment, in some way or other facilitating a process which without 

 it is extremely difficult to accomplish. Proteids may, however, 

 give rise to peptone without the presence of any pepsin at all, if 

 they be treated with strong acids, alkalies, boiling under high 

 pressure, putrefactive and other fermentative actions. This, to- 

 gether with the analogy suggested by the chemical details of the 

 amylolytic action of saliva, which one may say depends on an atom 

 of water being taken up, suggests that the change of proteid into 

 peptone is also hydrolytic, the peptones being simply an extremely 

 hyd rated form of proteid.* 



So far we have found that the action of the gastric juice affects 

 proteids alone. Its action on other constituents of food varies. 

 Gelatinous material is dissolved by the gastric digestion and ren- 

 dered incapable of forming a jelly ; its conversion into peptone 

 has, however, not been established. The connective tissue of meat 

 is therefore soon removed, and the muscle fibres fall asunder, the 

 sarcolemma is dissolved, and the muscle substance is converted 



*. Though proteids will not diffuse through a dead animal-membrane when 

 distilled water is used, a fair amount of diffusion takes place if a suitable 

 solution of common salt be employed instead of water. It must also be re- 

 membered that the gastric mucous membrane is a living active structure, 

 and that the fluid into which the albumins have to difliise may be regarded 

 as a salt solution. It is therefore quiteprobable that a considerable quantity 

 of albumin may be absorbed as such. The fact that peptone cannot be found 

 in any quantity in chyle or portal blood tends to prove that the albumin 

 does pass through the stomach wall without being changed into peptone. 



