POISON RESISTANCE. 99 



With naturally or artificially attenuated infectious 



mts of similar kind ; or 



2. With devitalized cultures of the micro-organisms 

 concerned. 



So far we know of two entirely different causes for this 

 immunity. 



A. — Poison Resistance (Specific Poison Immunity). 



After recovery from a series of infectious diseases (diph- 

 theria, tetanus, botulism) which have this in common, 

 that during their course very active poisons are produced 

 by the bacteria, there are found in the blood, and espe- 

 cially in the serum, characteristic substances which are 

 actively antagonistic to the poisons (antitoxins). The 

 antitoxic serum protects as well if it is used before the 

 introduction of the poisonous culture (it immunizes 

 passively) as if it is injected at the time of, or subsequent 

 to, the infection (it heals). It operates as well against 

 the introduction of the toxins of the concerned bacteria as 

 (in larger doses) against the introduction of living cul- 

 tures. 



As yet little is known regarding antitoxins, but they 

 are more resistant than the alexins to injurious influ- 

 ences. Thus the tetanus antitoxin bears very well 

 without being destroyed : a temperature of 60°, also 70° 

 to 80° for a shorter time, the action of sunlight (yellow 

 better than blue rays), and putrefaction. Brieger and 

 Ehrlich have obtained diphtheria antitoxin from the milk 

 of goats, immune to diphtheria, in solid form, — whether 

 it is an albuminous body or adheres to albuminous 

 bodies, is still unknown. The antitoxins are best separated 

 by means of zinc chlorid, but so far can not be freed 

 from the final traces of zinc (Brieger and Boer, Z. H. 

 xxi, 266). 



Regarding the action of antitoxins and toxins upon each 

 other the following is now known. As Behring and Kita- 

 sato supposed, a toxin solution in a test-tube with a suffi- 

 cient quantity of antitoxin added is completely inactive, 

 because toxin and antitoxin mutually neutralize each 

 other (somewhat as base and acid). Buchner explained 



