GASTEIC DIGESTION. 149 



rapily digesting proteid if acid be added to it, tends to show that 

 in these so-called mucous glands pepsin is also produced. 



The acid is found chiefly on the surface of the stomach. The 

 mode of its production seems distinct from that of pepsin, but is 

 not well understood. Although the deeper parts of the glands do 

 not give an acid reaction, while the neck and orifices of the gland 

 are distinctly acid, there is good reason for believing that this 

 manufacture of acid from the alkaline blood is really an active 

 process carried out by some glandular cells. 



It has been suggested that the cell elements which produce the 

 acid are the ovoid border-cells, from whence it rapidly passes to 

 the orifice of the glands. This view is supported by the alka- 

 linity of the pyloric end of the stomach where the border cells 

 are not found. In some animals the distinct distribution of the 

 different cell elements and the accompanying reaction of the 

 secretion are well marked. 



ACTION OF THE GASTRIC JUICE. 



The gastric juice has in the absence of mucus no effect on the 

 carbohydrates, and probably the amylolytic fermentation set up 

 by the saliva is impeded, if not completely checked, by the free 

 acid in the stomach. 



The gastric juice has no effect on pure fats, but it dissolves the 

 proteid frame-work of adipose tissue and thus sets the fats free, 

 which are then turned by heat to a liquid mass like oil. Upon 

 the albuminous bodies the gastric digestion produces a marked 

 effect. The proteids being colloid bodies cannot pass through an 

 animal membrane by the process called dialysis ; it has therefore 

 been assumed that they cannot be absorbed through the lining 

 membrane of the stomach. They are also often eaten in an in- 

 soluble form. To convert the insoluble and iudiffusible albumins 

 into a soluble and diffusible substance would obviously be a great 

 step towards their absorption. This power is ascribed to the gas- 

 tric juice. The steps of the process may be accurately followed 

 in a suitable glass vessel, irrespective of the stomach, by using 

 artificial gastric juice, and attending to the various conditions 



