THE EXISTENCE OF SENSITIZING SUBSTANCES. 223 



so kind as to allow us to take 3 to 4 c. c. of blood from two of the 

 convalescent cases of typhoid in his hospital service. Both these 

 women had shown the classical symptoms of typhoid fever. At 

 the time the blood was taken the temperature had been normal for 

 from 20 to 30 days. 



The sera obtained from the two patients were heated, together 

 with control sera from each of us, who have never had typhoid, to 

 56 degrees for a half hour. A small amount of one of the control 

 sera was kept unheated for alexin. 



The result of the experiment was very convincing. In tubes 

 containing alexin 0.2 c.c. (unheated human serum), emulsion of B. 

 typhosus (0.5 c.c.)* neither of our heated sera caused any fixation 

 of the alexin. Sensitized rabbit corpuscles added a few hours later 

 were hemolyzed as rapidly as in control tubes containing the sera 

 without bacterial emulsion. In the tubes containing human alexin, 

 typhoid bacillus, and either of the heated sera from typhoid con- 

 valescents, subsequently added sensitized corpuscles remained in- 

 tact for days. In similar mixtures of sera without bacilli, hemolysis 

 occurred with customary rapidity. 



Consequently, the power of causing the typhoid bacillusf to 

 absorb human alexin is very marked in the serum of patients con- 

 valescent from typhoid. $ 



It would be of interest to determine just how highly specific such 

 a serum is, particularly by comparing the reaction as between B. 

 typhosus and B. coli. The time in the course of the disease at which 

 this power appears in the serum is also of interest, but would neces- 

 sitate an examination of a large number of cases. Hitherto we 

 have had neither the time nor the material to consider these 

 problems. 



Serum of guinea-pigs vaccinated against B. proteus vulgaris. — The 

 method described for demonstrating the existence of a sensitizer by 



* An emulsion prepared by suspending a 24-hour agar culture of B. typhosus 

 in 5 c.c. salt solution of 0.7 per cent. 



t The culture of B. typhosus used was one that had been carefully controlled 

 by Dr. Binot of the Pasteur Institute, who was so kind as to give it to us. 



J These particular sera were only faintly agglutinative for B. typhosus. In 

 this connection the observations of Pfeiff er and Kolle may be recalled ; they showed 

 that the agglutinating power in such sera does not run parallel to the bactericidal 

 power. 



