296 METHODS OF OBTAINING THE GASTRIC JUICE. 



the wound in the abdominal walls. A short tube with a terminal plate is placed 

 in the fistula in such a manner that the plate lies in contact with the margin of 

 the mucous membrane. The tube possesses a screw-thread, upon which an appro- 

 priate cannula can be so screwed that the terminal plate lies upon the abdominal 

 wall outside of the margins of the wound. The parts are joined in the following 

 manner H -H. As a rule the opening of the cannula is corked. If in such 

 dogs the excretory ducts of the salivary glands are additionally ligated, unmixed 

 gastric juice is secured. 



According to C. A. Ewald and Leube, dilute gastric juice can be obtained from 

 human beings by introducing water into the empty stomach through a tube that 

 acts like a siphon, and withdrawing the fluid by siphonage after a short time. 



An important advance was made by Eberle, in 1834, who taught that artificial 

 gastric juice could be prepared by extracting pepsin from the gastric mucous 

 membrane by means of dilute hydrochloric acid. Dilute hydrochloric acid serves 

 for the extraction of the triturated gastric mucous membrane 0.088 per cent, for 

 the digestion of fibrin, 0.16 per cent, for the digestion of coagulated albumin 

 being added anew, in quantities of a half liter every six or eight hours. The later 

 extracts are even more active than the first. The fluid collected is filtered and 

 in it are placed, at the temperature of the body, the substances to be digested. 

 It is, however, necessary to add more hydrochloric acid from time to time. That 

 degree of acidity affects digestion most ^ favorably that most causes the proteids 

 to swell. According to Klug, gastric juice containing 0.6 per cent, of hydro- 

 chloric acid and o.i per cent, of pepsin is most effective. Pepsin from dogs is 

 especially active. Digestion pursues a favorable course between 37 and 40 C.; 

 while it ceases in the cold, as well as at higher temperatures. 



The hydrochloric acid employed may be replaced, to a certain extent, by 

 other halogen-acids, whose activity is inversely proportional to their molecular 

 weight ; further by from six to ten times as much lactic acid; by nitric acid; in 

 a much less effective manner, finally, by oxalic, sulphuric, phosphoric, acetic, 

 formic, succinic, tartaric, and citric acids. In general, the acids with greater 

 acidity act more powerfully, with the exception of sulphuric acid. The action of 

 the different acids varies, however, accordingly as fibrin, casein, solid or liquid 

 albumin is employed. 



v. Wittich showed that pure pepsin can be extracted from the gastric mucous 

 membrane by means of glycerin also. After cleaning the mucous membrane, it is 

 left in alcohol for twenty-four hours, then dried, pulverized and sifted, and then 

 extracted for a week in glycerin. On addition of alcohol to the filtered extract 

 pepsin is precipitated, and this, dissolved in dilute hydrochloric acid, yields active 

 gastric juice. 



The preparation of perfectly pure pepsin has been effected by W. Kiihne by 

 exposing comminuted pigs' stomachs to autodigestion with dilute hydrochloric 

 acid at the temperature of the body. The mass, which is for the most part liquefied, 

 is saturated with ammonium sulphate, by which pepsin and albumoses still present 

 are precipitated. The residue collected on the filter is again and if necessary 

 repeatedly digested in the incubator, after addition of dilute hydrochloric acid. 

 If, finally, all of the albumin has been converted into peptone, the pepsin alone is 

 precipitated by repeated saturation with ammonium sulphate, and is collected on 

 the filter. It is dissolved in water, its salts are removed by dialysis and it is finally 

 precipitated in a pure state by alcohol. Briicke had previously prepared pure 

 pepsin by causing a voluminous precipitate in the digestive mixture including the 

 pepsin, and separating the latter. Pekelharing found that a strongly active arti- 

 ficial gastric juice, on dialysis with water, caused the separation of a precipitate 

 of pepsin. 



In all the processes of extraction, the yield of pepsin is greatest when the 

 mucous membrane, protected from putrefaction, is exposed to the air for some 

 time, as subsequently propepsin and pepsin are formed in the gland-cells. 



Pure pepsin is a colloid substance. It does not yield the reactions 

 of albumin to the following tests: It does not respond to the xantho- 

 proteic test, is not precipitated by acetic acid and potassium ferrocyanid, 

 by tannic acid, mercuric chlorid, argentic nitrate or iodin. In other 

 respects it is to be included among the albuminoid substances. Pepsin, 

 when heated to a temperature of from 55 to 60 C. or above, in acid 

 solution, is rendered inactive. 



