2/4 LECTURES ON IMMUNITY 



as cyclamin, saponin, digitalin, solanin, cobra-venom, and 

 haemolytic sera, produce, when injected into living animals, 

 haemolysis, which is manifested by haemoglobinuria. " It 

 must, however, be stated that the actions of the haemo- 

 lysins in corpore are in no case limited to the erythro- 

 cytes." At all events, it seems prudent not to assume a 

 priori that the actions of poisons in vitro and in vivo are 

 identical. 



The best known of all the coagulating substances is ren- 

 net (or chymosin). It seems rather probable that the chief 

 action of rennet is analogous to that of peptic digestion, 

 and that the coagulation is a mere accidental property 

 belonging to the products of the digestion at higher tem- 

 perature (cf. p. 267). Be that as it may, the coagulation 

 is the property employed hitherto for the investigation of 

 the action of rennet. The coagulating power of rennet is 

 diminished by some normal sera, especially serum from 

 horses, as well as by immune-sera produced by the injection 

 of rennet into animals, 1 rabbits being especially adapted to 

 this purpose. 



Madsen and Walbum have investigated the neutralising 

 power of this " antirennet " and found that it behaves just 

 as antitetanolysin does against tetanolysin. The experi- 

 mental method was the following : Mixtures of 4 c.c. of 

 a i per cent solution of rennet and different quantities 

 (0.02-1 c.c.) of the antirennet-containing serum and of 

 physiological salt-solution were prepared so that the total 

 quantity was 5 c.c. These mixtures were held at room 



1 Morgenroth: {Centralbl. f. Bakteriologie, i. Abth. 26. 349, 1899, and 

 27. 721, 1900) was the first to prepare antirennet. He immunised goats 

 by the subcutaneous injection of rennet. After repeated injections the serum 

 of the goat contained antirennet. 



