926 THE EXTERNAL SECRETIONS 



mucus which acts as a protection for the underlying cells. In prac- 

 tically all cases of hyperchlorhydria, however, the secretion of mucus 

 is greatly diminished, without thus creating an especially favorable 

 condition for the formation of ulcers. Contrariwise, mucus may be 

 secreted in excessive amounts in the presence of formidable ulcers. 

 Another theory holds that the aforesaid resistance of the gastric wall 

 is due to the alkalinity of its constituent cells which tends to neutralize 

 the gastric juice anointing them. Going a step farther in this direc- 

 tion, we might say that the cause of the resistance of the gastric 

 mucosa against digestion lies in the normality of its life processes. The 

 latter consist in oxidations, and hence, it is evident that the pepsin 

 immediately exposed to them must be rendered inert by being oxidized. 

 In this connection it is of interest to note that the cells of the gastric 

 mucosa possess an intense power of oxidation. This observation 

 of Lillie^ is in accord with that of Burge,^ proving that pepsin is easily 

 destroyed by oxidation. Under normal conditions, therefore, a 

 balance is established between the intracellular oxidations and the 

 digestive action of the neighboring pepsin. Whenever this balance 

 is destroyed, the cells are digested with the formation of erosions of 

 varying size. 



These oxidative processes may be disturbed in different ways; 

 for example, by cutting off the blood supply of a particular area of 

 the stomach or by depressing the circulatory efficiency of the animal 

 as a whole. Thus, a local anemia may be established in consequence 

 of tumors, wounds, stricture of the pylorus and thrombosis; and a 

 general circulatory deficiency in consequence of hemorrhage, anemia, 

 poisons and toxins. 



The Regulation of the Secretion of Gastric Juice by Hormones 

 and Vitamines. — In general, it may be said that glands may be made 

 to secrete in two ways, namely, indirectly by means of chemical agents 

 contained in the blood, and directly by the stimulation of the nerve 

 fibers innervating the different cells. Eventually, of course, both types 

 of stimuli are conveyed to the cells, exciting their cytoplasm at first 

 hand. Agents which possess this stimulating action, most generally 

 arise elsewhere in the body and are brought to the gland in the blood- 

 stream. Thus, it has been found that the pituitary body gives rise 

 to an internal secretion which increases the flow of milk from the 

 mammary gland, and that the lining of the duodenum produces an 

 agent which initiates the flow of pancreatic juice. As far as the stom- 

 ach is concerned, Edkins^ has shown that the injection into the blood- 

 stream of broth, dextrin, peptone or acid does not augment the flow 

 of gastric juice, while an extract of the mucous membrane of the 

 pylorus invariably acts as a potent secretogogue. It is evident, there- 

 fore, that the mucosa of the stomach produces a hormone, known 



1 Am. Jour, of Physiol., vii, 1902, 413. 



2 Ibid., xxxvii, 1915.462. . 



3 Jour, of Physiol., xxxiv, 1906, 133. 



