HEMOLY8I8. 159 



toxins" in the serum, etc. There is reason to 

 believe that two or more different protective proc- 

 esses may come into operation at the same time 

 against a given infection. 



Regarding natural antitoxic immunity, it seems 

 probable that we have no example in which 

 the resistance can be satisfactorily explained solely 

 by the quantity of "antitoxins" which are dem- 

 onstrable in the serum ; rather we must assume the 

 existence of other means of destroying and resist- 

 ing toxins, as mentioned above. 



In order that a pathogenic organism may pro- 

 duce a progressively fatal disease in a susceptible 

 animal, the following obstacles must be sur- 

 mounted: The strong defenses of the body sur- 

 faces must first be overcome ; a local inflammatory 

 reaction which may have been excited must first 

 prove itself to be inadequate for the limitation of 

 the infection; there must be an insufficient supply 

 or insufficient activity of antimicrobic and anti- 

 toxic processes in the body fluids and cells. 



Other Properties of Normal Serums 



In addition to the bactericidal and antitoxic ac- 

 tion of many normal serums, they often possess 

 other characteristics which are of the highest in- 

 terest in the study of immunity. In earlier days 

 it had been noted that the transfusion of blood 

 from one species to another was often fatal to the 

 injected animal. Later investigations showed 

 that this was due to toxic substances in the trans- 

 fused blood ; substances which agglutinated and de- 

 stroyed the red blood cells of the injected animal. 

 The process, in which the hemoglobin is dissolved 

 out of the red blood cells, may be reproduced in 



