IMMUNITY 471 



case (positive result) there is, however, still the possibility that the 

 organism is devoid of pathogenic properties and has been destroyed by 

 the normal peritoneal fluid. A control experiment should accordingly 

 be made with '001 c.c. of normal serum in place of the anti-cholera serum. 

 If no alteration of the organism occurs with its use, then the conclu- 

 sion is that a true reaction has been given. Corresponding bacteriolytic 

 effects may be obtained by in vitro methods, introduced since Pfeiffer's 

 original method (p. 571). 



The serum of an animal immunised by the above method has 

 also marked agglutinative and other anti-bacterial properties 

 (p. 578) against the cholera spirillum, and these properties closely 

 correspond with Pfeiffer's reaction as regards specificity. Such 

 a serum has, however, little protective effect against the toxic 

 action of the dead spirilla, and Pfeiffer maintains that little or 

 no antitoxin to the endotoxin can be produced. On the other 

 hand, Macfadyen, by injecting the endotoxin derived from the 

 spirilla by grinding, obtained a serum which had antitoxic as well 

 as agglutinative and bacteriolytic properties (vide Immunity). 

 Metchnikoff and others have also obtained antitoxic sera which 

 act on the extracellular toxins. While it may be admitted 

 that antitoxins to some of the cholera toxins may be obtained, 

 yet Pfeiffer's position, that cholera anti-sera have little effect on 

 at least most of the endotoxins, cannot be said to be shaken. 

 It should be noted, however, that he disclaims having made the 

 general statement, often ascribed to him, that no antitoxins are 

 formed to endotoxins. 



The serum of cholera convalescents has been found to possess 

 protective and increased bactericidal action. These properties of 

 the serum may be present eight or ten days after the attack of 

 the disease, but are most marked four weeks after ; they then 

 gradually diminish. Specific agglutinative properties have, how- 

 ever, been detected in the serum of cholera patients at a much 

 earlier date, in some cases even on the first day of the disease, 

 though usually a day or two later. The dilutions used have 

 been usually 1 : 15 to 1 : 120, and these had no appreciable 

 effect on organisms other than the cholera spirillum (Achard and 

 Bensande). In some cases, however, the agglutinative property 

 may not appear. Variations in the opsonic index, analogous to 

 those in other diseases, have recently been observed in cholera, a 

 marked fall on the acute onset of the disease being a noteworthy 

 feature. 



Within recent times there have been introduced for therapeutic 

 purposes several so-called anti-sera which are supposed to be anti- 

 toxic as well as anti-bacterial, and of these the two most ex- 

 tensively used are those of Kraus and Schurupoff. Reports 



