540 APPENDIX 



with tubercle bacilli. When exudates, produced by virulent cultures of 

 these various organisms and properly sterilized, are injected with fresh 

 cultures into an animal death occurs in much shorter time than when 

 the organisms alone are injected. 



Moreover, it has been possible to immunize animals against these 

 various infections by repeated injections of the aggressin in the form of 

 exudates. This results in the formation of an " antiaggressin," which 

 opposes the action of the aggressin, thereby enabling the leukocytes to 

 take up the bacteria and thus to protect the animal. This has been 

 done in staphylococcus, dysentery, typhoid, cholera, pneumococcus, 

 and chicken cholera infections in animals. In addition a very marked 

 agglutinative property of the blood is acquired for the bacteria in the 

 animals so immunized. 



Experiments Devised by Ehrlich to Show the Nature of 



Hsemolysins. 



In order to give the student an idea of the methods employed by 

 Ehrlich in developing his doctrine of immunity, the classical series of 

 experiments made to show the nature of hsemolysins are here reproduced. 



Ehrlich asked himself two questions : (1) What relation does the hsemo- 

 lytic serum or its two active components, immune body and complement, 

 bear to the cell to be dissolved ? (2) On what does the specificity of this 

 hsemolytic process depend? He made his experiments with a hsemo- 

 lytic serum that had been derived from a goat treated with the red cells 

 of a sheep. This serum, therefore, was hsemolytic specifically for sheep 

 blood cells i. e., it possessed increased solvent properties exclusively for 

 sheep blood cells. Basing his reasoning on the side-chain theory, Ehrlich 

 argued as follows: "If the hsemolysin is able to exert a specific solvent 

 action on sheep blood cells, then either of its two factors, the immune 

 body or the alexin (complement) of normal serum, must possess a 

 specific affinity for these red cells." To show this he devised the follow- 

 ing series of experiments: 



EXPERIMENT 1. Ehrlich and Morgenroth, as already said, experi- 

 mented with a serum that was specifically hsemolytic for sheep blood 

 cells. They made this inactive by heating to 55 C., so that then it 

 contained only the substance sensibilatrice (immune body). Next they 

 added a sufficient quantity of sheep red blood cells, and after a time 

 centrifuged the mixture. They were now able to show that the red 

 cells had combined with all the substance sensibilatrice, and that the 

 supernatant clear liquid was free from the same. In order to prove 

 that such was the case they proceeded thus : To some of the clear cen- 

 trifuged fluid they added more sheep red cells; and, in order to reacti- 

 vate the serum, a sufficient amount of alexin in the form of normal 

 serum was also added. The red cells, however, did not dissolve there 

 was no substance sensibilatrice. The next point to prove was that 

 this substance had actually combined with the red cells. The red 



