306 IMMUNO-CATALYSIS 



required to neutralize the activity of rennin contained in 0.05 ml. 

 solution, and 0.025 ml. and 0.015 ml. of rennin solution were respec- 

 tively neutralized by 15 ml. and 10 ml. of immune serum. In control 

 experiments normal goat serum showed no effect on the coagulation of 

 milk by rennin. 



While the milk of cows and normal goats was coagulated with as 

 little as 1 part in 3,000,000, the milk of the goat immunized with 

 rennin did not coagulate until the concentration of added rennin was 

 1 part in 30,000; that is, 100 times more rennin was required to coagu- 

 late the milk of an immune goat than that of a normal goat. This was 

 regarded as a confirmation of the facts previously observed by Ehrlich 

 that the milk of immunized animals contains antitoxins, such as tet- 

 anus and diphtheria antitoxins. And the amounts of antitoxins and 

 antirennin were found to run parallel with the degree of immunization. 



e. Antibody Against Plant Rennin. In a subsequent study Mor- 

 genroth (1900) experimented with a plant rennin prepared from an 

 Italian plant, Cynara cardunculus, used for the preparation of cheese. 

 He obtained a partially purified enzyme preparation twenty times 

 weaker in activity than that of the animal rennin, and with this im- 

 munized a goat. Using 5 ml. of cow's milk, the immune goat serum 

 prepared against plant rennin neutralized 27 to 30 times more rennin 

 than was required by the control tube. The anti-rennin (plant) serum 

 did not neutralize the activity of animal rennin. Conversely the im- 

 mune goat serum against animal rennin did not neutralize the activity 

 of the plant rennin. These facts showed the serological specificity of 

 the animal and plant rennins. 



Thaysen (1915) prepared potent immune sera by injecting rennin 

 into rabbits. Those sera could be preserved for over a year without 

 observing any decrease in their specific activity. Tests were performed 

 similar to those used by Morgenroth. In inhibition experiments the 

 activity of 0.03 ml. of rennin solution was completely neutralized in- 

 stantaneously by 0.1 ml. of homologous immune rabbit serum at 20°C. 

 Normal serum showed no inhibitory action on rennin, or, if any, the 

 effect was not observed for four hours or longer. The instantaneous 

 action of the immune serum on rennin activity, as observed by Thay- 

 sen, agrees perfectly with the facts known at present. In serological 

 reactions 90 to 95 per cent of an antigen-antibody combination occurs 

 within the first few minutes. 



