188 IMMUNITY AND INFECTION 



the analogous selective behavior of various narcotics and alkaloids. 

 It seems probable, from the researches of these men, that the selective 

 action of poisons depends upon the ability, chemical or physical or both, 

 of the poisons to enter into combination with the specifically affected 

 cells. From the nature of the combinations formed, it seems not unlikely 

 that the physical factors, such as solubility in the cell plasma, may also 

 play an important part. 



Observations of a more purely bacteriological nature have tended 

 to bear out these conclusions-. Wassermann and Takaki,' for instance, 

 have shown that tetanus toxin, which specifically attacks the nervous 

 system, may be removed from solution by the addition of brain sub- 

 stance. Removal of the brain tissue by centrifugation leaves the solu- 

 tion free from toxin. In the same way it has been shown that hemo- 

 lytic poisons can be removed from solutions by contact with red 

 blood cells, but only when the red blood cells of susceptible species arc 

 employed. 



Similar observations have been made in the case of leukocidin, a 

 bacterial poison acting upon the white blood cells specifically.^ 



That bacterial poisons injected into susceptible animals rapidly 

 disappear from the circulation is a fact which bears out the view that 

 a combination between affected tissue and toxin must take place. 

 Donitz,' for instance, has shown that within four to eight minutes after 

 the injections of certain toxins, considerable quantities will have dis- 

 appeared from the circulation. Conversely, Metchnikoff * has ob- 

 served that tetanus toxin injected into insusceptible animals (lizards) 

 may be detected in the blood stream for as long as two months after 

 administration. 



1 Wassermann und Takaki, Berl. klin. Woch., 1898. 



2 Sachs, Hofmeister's Beitrage, 11, 1902. 

 'Donitz, Deut. med. Woch., 1897. 



* Metchnikoff , "L'immunit^ dans les malad. infect." 



