474 DIGESTION. 



Rennin or CHYMOSIN is the enzyme, which is especially character- 

 ized by the fact that it coagulates milk or casein solutions containing 

 lime in neutral or indeed faintly alkaline reaction. It must probably 

 be considered as a proteolytic enzyme. Rennin 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 mammals and in 

 birds it is seldom found, and in fishes hardly ever in the neutral infusion. 

 In these cases, as in man and the higher animals, a rennin-forming sub- 

 tance, a rennin zymogen, occurs, which is converted into rennin by the 

 action of an acid (HAMMARSTEN). HEDIN has obtained a retarding 

 solution by treating a neutral infusion of the stomachs of various animals 

 with dilute ammonia and then neutralizing. These solutions entirely 

 or partly retard the action of the rennin from the same animal and is 

 destroyed by acid with the setting free of rennin. HEDIN therefore 

 considers the rennin zymogen as a combination between rennin and an 

 inhibitory substance, in which combination the inhibitory body is 

 destroyed by treatment with acid; consequently the rennin appears in 

 an active form. 



According to BANG the rennin of the human and pig stomachs differs 

 from that of the calf's stomach in being much more resistant to acids, 

 more easily destroyed by ^alkalies, and that its action is much more 

 accelerated by calcium chloride than that from the calf's stomach. 1 

 Active rennin occurs in the human stomach under physiological condi- 

 tions, but may be absent under special pathological conditions. 2 



According to the experience of HAMMARSTEN the rennin of the pike 

 and of the dog differs from that of the calf, and HEDIN 3 finds in the specific 

 kind of inhibitory action of rennin produced by means of ammonia 

 treatment as well as by immune serum, a proof that the rennin enzyme 

 of different kinds of animals differ more or less from each other. In 

 regard to this inhibition see pages 62-64. 



Enzymes having a rennin action has also been found in the blood 

 and several organs of higher animals as well as in invertebrates. Sim- 

 ilar enzymes are also very widely distributed in the plant kingdom and 

 numerous micro-organisms have the ability to produce rennin. 



1 Deutsch. med. Wochenschr., 1899, and Pfluger's Arch., 79. 



2 Schumburg, Virchow's Arch., 97. A good review of the literature may be found 

 in Szydlowski, Beitrage zur Kenntnis des Labenzym nach Beobachtungen an Saug- 

 lingen, Jahrb. f. Kinderheilkunde (N. F.), 34. See also Lorcher, Pfluger's Arch., 69. 

 which also contains the pertinent literature. An excellent review of the literature 

 on rennin and its action may be found in E. Fuld, Ergebnisse der Physiol., 1, Abt. 1, 

 468. 



3 Hammarsten, Upsala Lakaref. forh. 8, 78 (1872). Zeitschr. f. physiol. Chem. 

 56, 18 (1908), 68, 119 (1910); Hedin, ibid. 72, 187, 74, 242, 76, 355 (1911), 77, 229 (1912). 



