84 ARTIFICIAL DIGESTION. AGENTS WHICH ARREST DIGESTION. [BOOK II. 



much more active if a stronger HC1, even up to 0'5 per cent., be 

 employed. 



Hydrochloric Hydrochloric acid may be replaced by other dilute 

 acid may be re- acids in the preparation of artificial gastric juice, as by 

 placed by other nitric acid, tribasic phosphoric acid, lactic acid, &c. 



t It appears that sulphuric, acetic, oxalic and tartaric 

 preparation of . , rr , , \ 



artificial gas- aclds act more feebly 1 . 



We usually determine that an artificial digestive 

 Determina- juice is possessed of proteolytic activity by placing it 

 Won of the j n an incubator, or in other ways maintaining it at a 

 artificial gaT temperature favourable to pepticproteolysis(35 50C.), 

 trie juice. an d then adding to it (a) a flocculus of well washed 



fibrin, preferably of fibrin which has been previously 

 swollen by digestion in cold dilute solution of hydrochloric acid ('1 per 

 cent.) : (6) thinly cut slices of coagulated white of egg : or (c) boiled 

 white of egg finely pounded in a mortar and pressed through a fine 

 sieve : and observing the time occupied in the solution of the proteids 

 used. A full description of the methods of determining the relative 

 amounts of pepsin in different solutions will be given in the sequel. 



Chemical Agents which influence Peptic Digestion 2 . 



All chemical agents which precipitate pepsin arrest digestion by 

 it, and generally the salts of the heavy metals exert this action, 

 as lead acetate, copper sulphate, mercuric chloride and alum. Neutral 

 salts of the alkalies and alkaline earths, as sodium chloride and 

 sulphate, magnesium sulphate, and potassium iodide hinder peptic 

 digestion. Arsenious acid is apparently without action. Hydriodic 

 and hydrobromic acids hinder peptic digestion. Sulphurous acid 

 arrests it. Hydrocyanic acid has but very slight action. 



Whilst tannic acid arrests digestion, some of the organic acids 

 which have most powerful action on organized ferments, hinder the 

 action of the peptic enzyme but little. Thus in small quantities 

 carbolic acid does not hinder digestion ; in medical practice it is 

 indeed found that carbolic acid often not only checks abnormal pro- 

 cesses of fermentation going on in the stomach, but that when 

 administered together with pepsin, it actually seems to aid this 

 body. 



Salicylic acid in large doses interferes with peptic digestion, 

 though according to Kiihne the pepsin is not destroyed even by 

 digestion for several days with large quantities of salicylic acid. 

 In diminishing the rapidity of peptic digestion salicylic acid is, how- 

 ever, certainly more powerful than carbolic acid. 



1 See many authorities quoted by Maly on this subject, Hermann's Handbuch, Vol. 

 v. Part ii. (1881), p. 72. 



2 The author has derived his information on this subject from Prof. Maly's article 

 in Hermann's Handbuch der Physiologic. 



