190 STUDIES IN IMMUNITY. 



add to the same dose of normal guinea-pig serum cholera vibrios 

 sensitized with cholera serum instead of normal vibrios. Under 

 such conditions the sensitized vibrios show rapid granular trans- 

 formation. If we then add to the mixture, as we did in the first 

 experiment, sensitized corpuscles we find that they remain indefi- 

 nitely intact. From this experiment we conclude that the alexin 

 necessary to destroy the corpuscles was used up before they were 

 introduced. In the presence of the cholera sensitizing substance 

 the alexin reacted with the vibrios and, in transforming them into 

 granules, was fixed by them. Consequently the alexin that unites 

 with sensitized vibrios and alters them is identical with the one that 

 produces hemolysis. 



EXPERIMENT. An emulsion of vibrios is prepared by suspending a 24-hour 

 agar culture in 5 c.c. of salt solution. The cholera sensitizing substance employed 

 is from a vaccinated rabbit and has been heated to 55 degrees. As a control for 

 this active serum normal rabbit serum, also heated to 55 degrees, is used. 



Mixture A. 0.5 c.c. of normal guinea-pig serum plus 0.3 c.c. of cholera sensi- 

 tizing substance plus 0.5 c.c. of vibrio emulsion. 



Mixture B. 0.5 C;C. of normal guinea-pig serum, 0.3 c.c. of normal rabbit 

 serum (55 degrees) plus 0.5 c.c. of vibrio emulsion. 



Mixture C. Identical with A but containing no vibrios. 



An hour's contact is allowed and there is then added to each mixture 0.2 of a 

 cubic centimeter of hemosensitizing substance (55 degrees) plus 2 drops of washed 

 rabbit blood.* 



The results of the experiments are as follows: the corpuscles are rapidly 

 destroyed in B and C, but remain intact in A. 



A similar experiment with the cells (bacteria and corpuscles) used 

 in the inverse order gives a similar result. We know from the work 

 of Ehrlich and Morgenroth as well as from our own that an alexin 

 that does not destroy given red blood cells is not fixed by them, but 

 is, on the contrary, fixed by cells that it can dissolve. 



An alexin that under normal circumstances has no effect on a 

 given species of corpuscles and therefore is not fixed by them is 

 fixed by these same corpuscles when they have been treated with 

 a suitable sensitizing substance. The fixation of the alexin by 



* In the majority of experiments we use previously washed blood instead of 

 simple defibrinated blood. This washing gives us rabbit blood corpuscles without 

 the addition of the serum present in defibrinated blood. The corpuscles are 

 washed by adding a relatively large amount of salt solution to a small amount of 

 defibrinated blood, centrifugalizing, and decanting the supernatant fluid. 



