A STUDY OF BLOOD MANUFACTURE 



89 



and a digestive ferment called pep 'sin. 1 If one examines with 

 a magnifying lens the mucous lining of the stomach, one sees 

 a countless number of small orifices that look like pinholes. 

 These are the pores through which gastric juice is dis- 

 charged from the gas'tric glands. The microscopic structure 

 of one of these glands is best studied in a thin section cut 

 at right angles to the surface through the wall near the car- 

 diac end of the stomach. The surface pore is the opening 

 from a compara- 

 tively short duct, 

 and connected with 

 this are two or 

 three tiny finger- 

 shaped recesses, 

 each one of which 

 is lined with a 

 single layer of cy- 

 lindrical cells (Fig. 

 31). Outside this 

 layer are other egg- 

 shaped cells, which 

 give to the gas- 

 tric glands their 

 peculiar beaded ap- 

 pearance. It is 

 probable that the 

 pepsin of the gastric juice is secreted by the cylindrical cells. 

 It is then discharged through the ducts when the food enters 

 the stomach. The origin of the hydrochloric acid has never 

 been satisfactorily explained; some physiologists believe, how- 

 ever, that it comes from the egg-shaped cells mentioned above. 

 Blood Supply of the Stomach. Beneath the mucous lining 

 of the stomach is a rich supply of blood vessels. The blood 

 brings to the stomach the chemical compounds necessary for 



1 In the gastric juice is also found another ferment called ren'nin, 

 which coagulates milk. 



Mucous lining 



containing 



glands. 



Submucous 

 layer contain- 

 ing blood ves- 

 sels and con- 

 nective tissue. 



Circular, ob- 

 lique, and 

 1 i gitudinal 

 muscles. 



Outer covering 

 of connective 

 tissue. 



FIG. 32. Section of Wall of Stomach. 



Magnified twelve times. Photographed through 

 the microscope. 



