450 DIGESTION. 



Chymosin (RENNIN) and Parachymosin. Besides the enzyme called 

 rennin (chymosin) which is found in the calf's stomach, there exists, 

 according to BANG/ another chymosin, the parachymosin, which is the 

 rennet enzyme of the pig and human stomach. This latter occurs in 

 the gastric juice of man under physiological conditions, but may be 

 absent under special pathological conditions (SCHUMBURG, BOAS, JOHN- 

 SON, KLEMPERER 2 ). Chymosin 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 substance, 

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

 of an acid (HAMMARSTEN). We have no knowledge as to whether the 

 rennet enzyme found in different animals is chymosin or parachymosin. 

 That the chymosin occurring in the calf's stomach is not identical with 

 that found in certain animals, for example the pike, follows without 

 question from the experience of HAMMARSTEN. Enzymes acting like 

 rennin are also found in the blood and several organs of higher animals, 

 as well as in invertebrates. Similar enzymes also occur widely diffused 

 in the plant kingdom, and numerous micro-organisms have the power 

 of producing rennin enzymes. Antibodies to the rennet enzymes, anti- 

 rennins, also occur in the animal kingdom, as shown by HAMMARSTEN 

 and RODEN in blood-serum, and may be produced in the animal body 

 by the introduction of rennin into the latter (MORGENROTH 3 ) . 



Rennin is just as difficult to prepare in a pure state as the other enzymes. 

 The purest rennin enzyme thus far obtained did not give the ordinary 

 protein reactions. On heating its solution rennin is more or less quickly 

 destroyed, depending upon the length of heating and upon the concen- 

 tration. If an active and strong infusion of the gastric mucosa in water 

 containing 3 p. m. HC1 is heated to 40-45 C. for 48 hours, the rennin 

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

 rennin can be obtained in this way. Rennin is characterized by its 

 physiological action, which consists in coagulating milk or a casein solu- 

 tion containing lime, if neutral or very faintly alkaline. The law of the 

 action of this enzyme is different from that of the action of pepsin. As 



1 Deutsch. med. Wochenschr., 1899, and Pfliiger'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 See R6d<n, Upsala Lakaref. Forh., 22; Morgenroth, Centrabl. f. Bakter., 26 

 and 27. 



