TOXINS AND ANTITOXINS 137 



formed by bacterial decomposition of proteids, the ptomains, 

 do not give rise to immune substances. 



TOXINS AND ANTITOXINS 



The first phase of immunity to be considered is the neutrali- 

 zation of toxin by antitoxin, since it is the most complete and 

 best understood of the reactions of immunity. In the preceding 

 chapter on the bacteria and their products the nature of the 

 true toxins was defined, and attention was called to the fact 

 that one of their most important characteristics is that immuni- 

 zation of animals against them leads to the accumulation in the 

 blood of substances capable of completely neutralizing their 

 poisonous action. Such true toxins are produced especially by 

 the diphtheria bacillus and the tetanus bacillus, also, but less 

 strikingly, by B. pyocyaneus, B. botulinus, and possibly by a 

 few others. In addition to these, numerous bacteria produce 

 hemolytic poisons which seem to have properties similar to the 

 toxins ; and there are also toxins produced by plants (abrin, 

 ricin, crotin, and mushroom poisons) and by animals (snake 

 venom, scorpion and spider toxin, and eel serum). Against all 

 of these, true antitoxins may be obtained by the immunization 

 of animals. 



Ehrlich's Conception of Toxins and Antitoxins. 

 According to Ehrlich's theory, the action of toxins upon cells 

 is purely chemical. A toxin unites with a cell because some 

 chemical group in the molecule of toxin has a chemical affinity 

 for some particular group in the cell protoplasm. For con- 

 venience in description names have been given to these groups ; 

 the group of the toxin that combines with the cell has been 

 called the haptophorous group, or haptophore, while the group 

 in the protoplasm that combines with the toxin is known as the 

 receptor. 1 It has been found that after being kept for some 

 time, or when placed under certain unfavorable conditions, the 

 toxin loses its poisonous properties without losing its power to 

 combine with cells, as shown by the fact that immunization with 

 such altered toxin gives rise to the formation of antitoxin. 



1 Ehrlich has used certain diagrams to illustrate these various groups and 

 their relations to the cells and to one another, which are generally used in 

 explaining his theory. From a teaching standpoint they have seemed to be 

 undesirable, in that the student soon comes to ascribe physical properties and 

 appearances to what should be considered as chemical combinations. The 

 toxophore group becomes " the black fringed end of the toxin," etc. To one 

 accustomed to thinking in chemical terms there is no difficulty in following 

 the literature and understanding the reactions as chemical reactions, which 

 they are. 



