GASTKIC DIGESTION. 353 



neutralized, the fibrin will regain its original appearance. If tube No. 3, which 

 contained the neutralized gastric juice, be acidulated to proper degree, the fibrin 

 will be dissolved. If tube No. 2 is neutralized, there will be a precipitate varying 

 in amount with the duration of the digestion. If that precipitate be filtered off, 

 the filtrate will still show the presence of a proteid body. 



The results of gastric digestions are. thus, not dependent upon the 

 acidity of the gastric juice alone, for we find that when the neutraliza- 

 tion product is filtered off there still remains in solution in the filtrate 

 a large quantity of proteid matter. This substance is termed peptone, 

 and has the same elementaiy composition as albumen and gives most of 

 the proteid reactions, it, however, differing from the ordinan r proteids 

 in several respects. In the first place, solutions of peptone diffuse readily 

 and are readily filtered. Tlie} r are not precipitated by boiling and nitric 

 acid, acetic acid and potassium ferrocyanide, and saturation with com- 

 mon salt. They are precipitated from neutral or faintly acid solutions 

 by mercuric chloride, tannic acid, bile acids, and phosphowolframic acid ; 

 they will yield the Millon's and xanthoproteic tests, and with caustic soda 

 or potash and a small quantity of cupric sulphate they give a beautiful 

 purple-red color instead of the violet yielded by other albuminous bodies 

 (Biuret test). They rotate the plane of polarized light to the left. When 

 injected into the blood they do not appear in the urine, as is the case 

 with egg-albumen, but when injected in large amounts produce the S3^mp- 

 toms of a narcotic poison and prevent coagulation of the blood. When 

 dried, peptones are amorphous, transparent, 3^ello wish-white, hygroscopic 

 powders, while when freshly precipitated they closely resemble coagu- 

 lated casein in appearance. 



When proteids are subjected to the action of gastric juice, the acid 

 first transforms the albuminous bodies into a substance analogous to acid 

 albumen, termed parapeptone, this substance thus standing midway 

 between the albumen and peptone. By the continued effect of the action 

 of the gastric juice, principally through the influence of the pepsin, the 

 parapeptone passes into a true soluble peptone, its formation being due 

 to the taking up of a molecule of water. Under the influence of the 

 hydrotytic ferment of pepsin, the greater the amount of pepsin, within 

 certain limits, the more rapidly the solution takes place, although it 

 seems that the pepsin is not used up in the process of gastric digestion ; 

 and if the degree of acidity be kept uniform, almost unlimited amounts 

 of albumen' may be digested by a small amount of pepsin. Large 

 amounts of peptones appear to interfere with the digestion of albuminous 

 bodies ; but if the peptones are removed as rapidly as formed, digestion 

 may go on until all the albumen is converted into peptones, or until the 

 acidity has disappeared. 



The gastric juice only digests the albuminous constituents of food, 

 vegetable albuminoids being digested in the same manner and with the 



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