400 STUDIES IN IMMUNITY. 



monopolize the alexin. As Muir and Browning have correctly 

 stated, the serum is antagonistic because it prevents the fixation of 

 the alexin on the sensitized cells, and this antagonism is overcome 

 only when the avidity of the cells for the alexin is very marked, 

 namely, when the cells are strongly sensitized or when the absorp- 

 tion of alexin is favored by the addition of salt solution. 



Sachs' experiment, which deals with the antagonistic action of 

 normal rabbit serum against the hemolysis of bovine corpuscles 

 treated with a small amount of sensitizer (the serum of a rabbit 

 immunized against bovine blood) in the presence of alexin (fresh 

 guinea-pig serum) is a suitable one for the study that concerns us. 

 It will be well to consider our experiment somewhat in detail in 

 order to deal with Sachs' explanation of a similar experiment in 

 which normal rabbit serum was also employed.* The following 

 experiment shows that moderately sensitized corpuscles are hemo- 

 lyzed by alexin if the medium in which they are suspended contains 

 a relatively large amount of salt solution, whereas they remain intact 

 or are affected only very slowly, if the surrounding fluid contains 

 less salt solution and a correspondingly increased amount of normal 

 rabbit serum (heated to 56 degrees). 



Tube A contains 0.6 of a cubic centimeter of physiological solu- 

 tion (NaCl, 0.9 per cent) ; Tube B, 0.3 of a cubic centimeter of salt 

 solution plus 0.3 of a cubic centimeter of normal rabbit serum 

 (56 degrees for one-half hour). To each tube is added 0.05 of a 

 cubic centimeter of alexin (fresh normal guinea-pig serum) and 0.3 

 of a cubic centimeter of salt solution containing 10 per cent of 

 moderately sensitized bovine blood. f 



Tubes A and B are placed in a thermostat (35 degrees). Hemoly- 



* Rabbit serum is used, as it is only faintly sensitizing for ox corpuscles. It is 

 evident that if the normal serum has a distinct sensitizing effect on the corpuscles 

 under consideration it cannot be considered as an inert medium. Theoretically 

 there is perhaps no absolutely inert serum, but its sensitizing effect on a given 

 bacterium or alien red blood cell is frequently so slight as to be imperceptible, as 

 is the case in the present instance. 



t This blood is prepared as follows: To 1 c.c. of bovine blood (previously 

 washed to remove all serum) is added 9 c.c. of salt solution, and 0.1 of a cubic 

 centimeter of serum (56 degrees) from a rabbit immunized against bovine blood. 

 After shaking and allowing contact for 20 minutes the tube is centrifugalized and 

 the supernatant fluid removed. To the sediment of corpuscles 10 c.c. of salt 

 solution is then added. 



