METHODS OF OBTAINING GASTEIC JUICE. 247 



165. METHODS OF OBTAINING GASTRIC JUICE. Historical Spallanzani caused 

 .starving animals to swallow small pieces of sponge enclosed in perforated lead capsules, and 

 after a time, when the sponges had become saturated with gastric juice, he removed them from 

 the stomach. To avoid the admixture of saliva, the sponges are best introduced through an 

 opening in the oesophagus. Dr Beaumont (1825), an American physician, was the first to 

 obtain human gastric juice, from a Canadian named Alexis St Martin, who was injured by a 

 gun-shot wound, whereby a permanent gastric fistula was established. Various substances 

 were introduced through the external opening, which was partially covered with a fold of skin, 

 and the time required for their solution was noted. Bassow (1842), Blondlot (1843), and Bar- 

 deleben (1849) were thereby led to make artificial gastric fistula?. 



Gastric Fistula. The anterior abdominal wall is opened by a median incision just below the 

 ensiform cartilage, the stomach is exposed, and its anterior wall opened and afterwards stitched 

 to the margins of the abdominal walls. A strong cannula is placed in the fistula thus formed. 

 The tube is kept corked. If the ducts of the salivary glands be tied, a perfectly uncomplicated 

 object for investigation is obtained. 



According to Leube, dilute human gastric juice may be obtained by means of a syphon-like 

 tube introduced into the stomach. Water is introduced first, and after a time it is withdrawn. 



An important advance was made when Eberle (1834) prepared artificial gastric juice, by 

 extracting the pepsin from the gastric mucous membrane with dilute hydrochloric acid. Four 

 litres of solution of hydrochloric acid, containing 4 to 8 c.c. HC1 per 1000, are sufficient to extract 

 the chopped-up mucous membrane of a pig's stomach. Half a litre is infused with the stomach and 

 renewed every six hours. The collected fluid is afterwards filtered. The substance to be digested 

 is placed in this fluid, and the whole is kept at the temperature of the body, but it is necessary 

 to add a little HC1 from time to time {Schwann). The HC1 may be replaced by ten times its 

 volume of lactic acid and also by nitric acid ; while oxalic, sulphuric, phosphoric, acetic, formic, 

 succinic, tartaric, and citric acids are much less active ; butyric and salicyclic acids are inactive. 



Von Wittich's Method. (a) Glycerine extracts pepsin in a very pure form. The mucous 

 membrane is rubbed up with powdered glass until it forms a pulp, mixed with glycerine, and 

 allowed to stand for eight days. The fluid is pressed through cloth, and the filtrate mixed with 

 alcohol, thus precipitating the pepsin, which is washed with alcohol and afterwards dissolved in 

 the dilute HCl, to form an artificial digestive fluid, (b) Or the mucous membrane may be 

 placed for twenty-four hours in alcohol, and afterwards dried and extracted for eight days with 

 glycerine, (c) Win. Roberts has used other agents for extracting enzymes ( 148). 



Preparation of Pure Pepsin. Briicke pours on the pounded mucous membrane of the pig's 

 stomach a 5 per cent, solution of phosphoric acid, and afterwards adds lime-water until the 

 acid reaction is scarcely distinguishable. A copious precipitate, which carries the pepsin with 

 it, is produced. This precipitate is collected on cloth, repeatedly washed with water, and 

 afterwards dissolved in very dilute HCl. A copious precipitation is caused in this fluid, by 

 gradually adding to it a mixture of cholesterin in four parts of alcohol and one of ether. The 

 cholesterin pulp is collected on a filter, washed with water containing acetic acid, and after- 

 wards with pure water. The cholesterin pulp is placed in ether to dissolve the cholesterin, and 

 the ether is then removed. The small watery deposit contains the pepsin in solution. 



Pepsin so prepared is a colloid substance ; it does not react like albumin with 

 the following tests, viz.: It does not give the xanthroprotein reaction ( 248), is 

 not precipitated by acetic acid and potassium ferrocyanide, nor by tannic acid, 

 mercuric chloride, silver nitrate, or iodine. In other respects it belongs to the 

 group of albuminoids. It is rendered inactive in an acid fluid by heating it to 

 55 to 60 C. 



166. PROCESS OF GASTRIC DIGESTION. [In the process of gastric 

 digestion we have to consider 



1 . The secretion of gastric juice and its action on food. 



2. The absorption of the products of this digestion. 



3. The movements of the stomach itself.] 



Chyme. The finely divided mixture of food and gastric juice is called chyme 

 The gastric juice acts upon certain constituents of chyme. 



I. Action on Proteids. Pepsin and the dilute hydrochloric acid, at the 

 temperature of the body, transform proteids into a soluble form, to which Lehmann 

 (1850) gave the name of " peptone" ( 249, III.). Fibrin (or coagulated pro- 

 teids) first becomes clear and swollen up. 



[It is commonly stated that the first product formed during the gastric digestion 

 of proteids is syntonin or para-peptone, then hemi-albumose or pro-peptone, and 



