INFECTION AND IMMUNITY. 569 



stages of degeneration. The different species of bacte- 

 ria vary greatly with regard to their proneness to auto- 

 lysis. In some of them for instance, raicrospira comma, 

 bacillus typhosus, etc. the autolysis occurs quite early. 

 The poisonous substances contained in the bodies of the 

 organisms thereby pass into solution. One finds in ni- 

 trates of relatively young cultures some poisonous action, 

 which is still greater in nitrates from old cultures. Other 

 bacteria, as for instance, bacterium tuberculosis, show 

 great resistance to autolysis, and in consequence culture 

 filtrates contain only a small quantity of poisonous 

 substances. 



The poisonous substances found in culture filtrates 

 were at first assumed to be secretory products of the 

 bacteria, and were regarded as true toxin formations. 

 If we characterize toxins as having the property, in def- 

 inite doses, of bringing about the death of an animal, we 

 find that the endotoxins also have this property. We 

 have also characterized the toxins with the property of 

 bringing about an active immunity in animals when they 

 are injected in sublethal doses, and that the serum of 

 such animals when injected into normal animals protects 

 them against the minimum fatal dose of the toxin that 

 is, it brings about a passive immunity. On the other 

 hand, the injection of the endotoxins results in the induc- 

 tion of bactericidal immunity with the formation of 

 amboceptors of a specific character. 



THE POINT OF ACTION OF TOXIN AND ENDO- 

 TOXIN. With regard to the point of action of the 

 toxins the experiments of Wasserman and others in- 

 dicate that as far as tetanus toxin is concerned this 

 poison has a direct affinity for nerve cells. With regard 

 to diphtheria toxin one sees, on making a postmortem 



