202 STUDIES IN IMMUNITY. 



active against guinea-pig alexin it has no effect on rabbit alexin. 

 Experimental details follow: 



An emulsion of sensitized cholera vibrios^, prepared by suspending an agar 

 culture in 10 c.c. of salt solution, and adding 2 c.c. of cholera serum from a rabbit 

 heated to 56 degrees, is used. 



I. MIXTURES CONTAINING SENSITIZED VIBRIOS. 



a. Fresh normal guinea-pig serum, 0.2 c.c.; antitoxin (55 degrees), 0.4 c.c. 



b. Fresh normal guinea-pig serum, 0.2 c.c. ; normal rabbit serum (55 de- 

 grees), 0.4 c.c. 



c. Fresh normal rabbit serum, 0.2 c.c.; antitoxin (55 degrees), 0.4 c.c. 



d. Fresh normal rabbit serum, 0.2 c.c. ; normal rabbit serum (55 degrees) ,0.4 c.c. 

 To each of these four mixtures 0.2 c.c. of an emulsion of sensitized vibrios is 



then added. The mixtures are left for an hour at 37 degrees. Granular trans- 

 formation is complete in mixtures 6, c, and d. The vibrios in mixture a, con- 

 taining guinea-pig alexin neutralized by antitoxin, on the contrary, have kept 

 their normal appearance. 



II. MIXTURES CONTAINING SENSITIZED BLOOD. 



This blood consists of 0.2 of a cubic centimeter of rabbit blood (previously 

 washed in salt solution) plus 1 c.c. of hemolytic serum heated to 55 degrees. 



e. Identical with a. 



f. Identical with 6. 



g. Identical with c. 



To each of these mixtures 0.1 c.c. of the sensitized blood is added. The cor- 

 puscles are rapidly dissolved in/, less rapidly in g and remain intact in c. 



For the sake of completeness we may mention that the bacteri- 

 cidal effect is evident, not only by granular transformation of the 

 vibrios, but by their complete destruction, as shown by inoculating 

 agar tubes with the mixtures. In this way we find that a small 

 amount of sensitized vibrios mixed with normal guinea-pig serum 

 plus normal rabbit serum (55 degrees) becomes completely sterile. 

 The same dose of- vibrios mixed with guinea-pig serum plus anti- 

 toxin from the rabbit (55 degrees), on the contrary, remains alive; 

 cultures from this mixture on gelatin at intervals show numerous 

 colonies. 



The specificity of the anti-alexic action of the antitoxin. Our anti- 

 toxin neutralizes the alexin of guinea-pig serum. We have already 

 noted that it has no effect on the alexin of rabbit serum. Does it 

 affect the alexins in sera from other animal species? This may be 

 answered experimentally by adding doses of fresh serum from differ- 

 ent animals to a mixture composed as follows : 



