IMMUNITY. 187 



been shown in the case of tetanus toxin. The filtrate from 

 cultures of tetanus bacilli will kill guinea-pigs, presumably 

 by damage to the central nervous system. The same filtrate 

 rubbed up with brain or spinal cord has been found to have 

 lost its toxic proporties. It may be assumed that the poison 

 has combined with the protoplasm of the cells. 



Bacteriolysis. Although the hypothesis of Ehrlich just 

 stated may seem very complicated, more recent studies along 

 similar lines have led to conceptions so intricate, that they 

 can be followed only with the greatest difficulty. The 

 nomenclature of this subject has also become extremely 

 involved, as different words have often been coined to con- 

 vey a similar idea. In other cases a single word has been 

 used in different senses. 



The problems we have still to consider relate to the bac- 

 teria which do not produce soluble toxins. In infections 

 with these organisms, attempts to make protective or cura- 

 tive substances analogous to antitoxins have met with little 

 success. The outlook for better results in the future is 

 promising. 



The agencies which lead to the destruction of bacteria 

 during the progress of an infectious disease have been 

 studied chiefly in experimental infections in the lower ani- 

 mals. There are numerous bacteria, such as the spirillum 

 of cholera, bacillus of typhoid and bacillus coli communis, 

 injection of which may produce a fatal septicemia in ani- 

 mals. It also usually is possible to render animals 

 immune to them by injections of the dead bacteria, or 

 small doses of living bacteria, or the two in succession. 

 When an animal has been immunized in this manner, in- 

 jection of living cultures of the same kind is followed by 

 destruction of the bacteria injected. This phenomenon 

 appears to depend on the combined action of two substances. 

 Neither of these is effective without the other. The actual 



