284 STUDIES IN IMMUNITY. 



serum, 56 degrees, and to tube B, 2 c.c. of normal rabbit serum, 

 56 degrees. Half an hour later the two tubes are filled with salt 

 solution, shaken and centrifugalized. The supernatant fluids are 

 pipetted off and the sedimented corpuscles in each tube are sus- 

 pended in 3 c.c. of salt solution. These two corpuscle suspen- 

 sions differ only in that the first corpuscles are laden with specific 

 sensitizer. We may then prepare the following mixtures : 



Tube a. Sensitized blood, 0.1 c.c. ; Guinea-pig > rabbit antiserum, 56 degrees, 

 0.3 c.c. 



Tube b. Same as last, but containing 0.3 c.c. of normal guinea-pig serum, 

 56 degrees, instead of antiserum. 



Tubes c and d. Same as "a" and "b" respectively, but containing non- 

 sensitized blood in place of sensitized blood. 



One hour later 0.1 of a cubic centimeter of guinea-pig alexin (fresh serum) is 

 added to each tube. 



It is found that hemolysis takes place rapidly in tube "b." In 

 tubes "a," "c," and "d" there is no hemolysis even after 24 hours. 

 The lack of hemolysis in "a" is due to the neutralization of the 

 sensitizer by the antiserum, as may be shown by adding a small 

 amount of rabbit > ox serum, 56 degrees, which at once produces 

 hemolysis. The same results are obtained if we use any other 

 alexin (for example, human serum) that is not affected by the anti- 

 serum. 



This method of experimentation allows us to measure the anti- 

 sensitizing power of the antiserum. We may add in place of 0.3 

 of a cubic centimeter of pure antiserum to 0.1 of a cubic centimeter 

 of sensitized blood, 0.3 of a cubic centimeter of a dilution of anti- 

 serum in a greater or less amount of heated normal guinea-pig 

 serum. On trial we find that the antisera from different guinea- 

 pigs vary much in potency. The antisensitizing property of anti- 

 serum is frequently so strong that 0.1 of a cubic centimeter will 

 suffice to protect 0.1 of a cubic centimeter of sensitized blood from 

 the alexin. 



Having settled on our technic, we may now consider certain 

 questions that naturally arise concerning antisensitizers : Certain 

 of the questions (B, C, D and E) relate particularly to the effect of 

 the antiserum on the sensitizer; others (A and F) relate rather to 

 the origin of and the variations in antibodies. 



(A) Is an antiserum obtained by immunizing an animal of 



