GASTRIC DIGESTION. 161 



pieces of proteid have been reduced to a pulp, composed of 

 minute particles ; these are kept in constant motion by the gastric 

 walls, and thus are repeatedly brought in contact with fresh sup- 

 plies 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, 

 together 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 hydrolitic, the peptones being simply 

 an extremely hydrated 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 

 into true peptone. The delicate sheets of elastic tissue, such as 

 basement membranes and those of small vessels, are dissolved, but 

 larger masses of yellow elastic tissue are not affected by the gas- 

 tric digestion. The horny part of the epidermis, hairs, etc., are 



* 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 remembered that the gastric mucous membrane is a living active 

 structure, and that the fluid into which the albumins have to diffuse may 

 be regarded as a salt solution. It is, therefore, quite probable that a con- 

 siderable 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. 

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