184 PHYSIOLOGICAL CHEMISTRY. 



here a proof of the existence of a paired acid, called by C. SCHMIDT 

 pepsin hydrochloric acid. 



It has been further suggested that this hypothetical acid is possibly decom- 

 posed into pepsin and a free acid, which in statu nascendi dissolves proteids 

 to a certain degree. The pepsin set free reunites with a new portion of acid, 

 forming pepsin hydrochloric acid, and in contact with proteids is further 

 decomposed as above described. It is hardly necessary to mention that this 

 statement is only an unproved hypothesis. 



Rennet or CHYMOSIN (DESCHAMPS) is the second enzyme of the 

 gastric juice. According to BOAS, it is found in human gastric 

 under physiological conditions, but may be absent under special 

 pathological conditions, such as carcinoma, atrophy of the mucous 

 membrane, and certain chronic catarrhs (BOAS, JOHNSON, KLEM- 

 PEKER). It is habitually found in the neutral, watery infusion of 

 the fourth stomach of the calf and sheep, especially in an infusion 

 of the fundus part. In other mammalia and in birds it is seldom 

 found, and in fishes hardly ever in the neutral infusion. Instead 

 of this rennet-forming substance a rennet zymogen, from which the 

 rennet is formed by the action of an acid is always found. 



Kennet is just as difficult to prepare in a pure state as the other 

 enzymes. The purest rennet enzyme thus far obtained did not give 

 the ordinary albumin reactions. On heating its solutions it is de- 

 stroyed, and indeed more easily in acid than in neutral solutions. 

 If an active and strong infusion of a mucous coat in water contain- 

 ing 3 p. m. HC1 is heated to 37-40 C. for 48 hours, the rennet is 

 destroyed, while the pepsin remains. A pepsin solution free from 

 rennet can be obtained in this way. Rennet is characterized by its 

 physiological action, which consists in coagulating milk or a casein 

 solution containing lime, if neutral or faintly alkaline. 



Kennet may be carried down by other precipitates like other 

 enzymes, and thus may be obtained relatively pure. It may also be 

 obtained, contaminated with a great deal of proteids, by extracting 

 the mucous coat of the stomach with glycerin. 



A comparatively pure solution of rennet may be obtained in the 

 following way. An infusion of the mucous coat of the stomach in 

 hydrocholoric acid is prepared and then neutralized, after which it 

 is repeatedly shaken with new quantities of magnesium carbonate 

 until the pepsin is precipitated. The filtrate, which should act 

 strongly on milk, is precipitated by basic lead acetate, the preci- 

 pitate decomposed with very dilute sulphuric acid, the acid liquid 

 filtered and treated with a solution of stearin soap. The rennet is 



