72 PA THOGENIC BA CTERIA. 



manner, and must call attention to the fact that their 

 operation is in no way analogous to chemical neutraliza- 

 tion. From mixtures of toxin and antitoxin the un- 

 changed poison has been recovered. The effect of an 

 antitoxin, unlike that of a toxo-phylaxin, seems to be a 

 biologic one, by which the tissues are so stimulated as to 

 endure the action of a substance ordinarily disorganizing 

 in effect. 



Buchner and Roux have both pointed out that when 

 the toxins and antitoxins are mixed and introduced into 

 animals of greater susceptibility than are ordinarily used, 

 the presence of an unaltered toxin can easily be demon- 

 strated. 



According to Buchner, the antitoxins differ from the 

 alexins in being new substances in the blood, in being 

 without germicidal or chemical neutralizing power against 

 the toxins, and in being stable compounds which can 

 resist heat to 75 C., can resist a reasonable amount of 

 exposure to light, and which are not altered by decompo- 

 sition of the substances containing them. 



The antitoxins are specific for one poison only. Ehrlich 

 found that antiricin was powerless against abrin, and vice 

 versd. Diphtheria antitoxin is of no avail against tetanus, 

 and vice versd. 



The immunity which the antitoxins produce is fuga- 

 cious, varying considerably according to the particular 

 substance employed. As a rule, it is limited to a few 

 months at least in the case of such antitoxins as we can 

 produce experimentally. 



From all that has gone before it must be clear to the 

 reader that no single theory thus far advanced can ex- 

 plain immunity. Acquired immunity may depend in 

 the great majority of cases upon antitoxins, but as yet 

 we have no satisfactory explanation of natural immunity. 

 The humoral theory may be applicable in some cases ; in 

 others one cannot deny the importance of the role played 

 by the phagocytes. 



