220 STUDIES IN IMMUNITY. 



The following mixtures were then prepared in test tubes : 



(a) Alexic serum, 0.2 c.c.; emulsion of plague bacilli, 0.4 c.c.; 

 antiplague serum, 56 degrees, 1.2 c.c. 



(b) Same as "a," with normal horse serum, 56 degrees, replacing 

 the antiplague serum. 



(c) Same as u a," but containing no emulsion of plague bacilli. 



(d) Same as "b," but containing no emulsion of plague bacilli. 

 Each of these four mixtures contains the same amount of alexin 



(normal guinea-pig serum). 



(e) Emulsion of plague bacilli, 0.4 c.c.; antiplague serum, 56 de- 

 grees, 1.2 c.c. 



(f) Emulsion of plague bacilli, 0.4 c.c.; normal horse serum, 

 56 degrees, 1.2 c.c. 



These two tubes are the same as "a" and "b "respectively, with- 

 out alexin. 



The mixtures are left at room temperature (15 to 20 degrees) for 

 about 5 hours. To each tube in turn is added 0.2 of a cubic cen- 

 timeter of a mixture composed of 2 cubic centimeters of serum 

 from a guinea-pig immunized against rabbit blood and previously 

 heated to 55 degrees, and 20 drops of defibrinated rabbit blood.* 

 In other words, each tube receives 2 drops of well-sensitized blood. 



The result of the experiment is as follows: 



Hemolysis takes place rapidly and nearly simultaneously in 

 tubes "b," "c," and "d." In ten minutes no intact corpuscles 

 remain. In tube "a," containing alexin, bacilli and antiplague 

 serum, no hemolysis occurs. The corpuscles also remain intact in 

 tubes "e' 7 and "f," to which no alexin was added. We find then, 

 first, that the plague bacillus mixed with normal horse serum does 

 not absorb alexin; and second, that the bacillus with antiplague 

 serum from the horse does absorb alexin with avidity; and third, 

 that antiplague serum alone has no effect on the alexin. 



Consequently we must conclude that the serum of a horse vac- 



* As already mentioned in previous articles, blood that has been washed in salt 

 solution is generally used in experiments of this nature. 1 to 2 c.c. of defibrinated 

 blood is placed in a centrifuge tube and the level marked on the glass. After 

 centrifugalization the supernatant fluid is drawn up with a bulb pipette, leaving 

 the deposited corpuscles. Enough salt solution is added to restore the blood to its 

 original level. This constitutes defibrinated blood with the serum replaced by 

 salt solution, in other words, containing no alexin. 



