130 PROPERTIES OF ILEMOLYTIC SERA 



affected by lysis. Accordingly, in such a case, if the recep- 

 tors are retained by the filter the molecules of immune-body 

 which readily pass through in the free condition should be 

 retained also. This is found to be the case. The suspension 

 of red corpuscles is treated with seven hsemolytic doses of 

 immune-body, and the corpuscles are washed and centri- 

 fugalized repeatedly to remove the uncombined immune- 

 body ; they are then lysed with a minimum dose of comple- 

 ment. Part of the fluid is filtered, and we then test how 

 much immune-body can be obtained from the unfiltered 

 and filtered fluid respectively by placing red corpuscles in 

 it for an hour at 37 and then adding complement. In the 

 case of the unfiltered fluid a full dose of immune-body can 

 be obtained ; this is obtained by dissociation from the 

 combination receptor + immune-body ; from the filtrate 

 only a tenth of a dose is obtainable. But why should any 

 immune-body be obtained, seeing that the receptors do not 

 pass through the filter, and the immune-body is combined 

 with them ? The answer is that a certain amount of 

 immune-body dissociates from the red corpuscles at 37 C. 

 when they are washed and fresh salt solution is added, and 

 this small amount of free immune-body passes through the 

 filter ; in other words, the combination of immune-body 

 with red corpuscles is not in equilibrium when the fluid 

 is free from immune-body, and a small fraction of the latter 

 dissociates. This can easily be proved by taking red 

 corpuscles combined with several, say eight doses of immune- 

 body, and washing them repeatedly in salt solution to 

 remove the uncombined immune-body. The corpuscles are 

 then divided into two equal portions and fresh salt solution 

 is added. One portion (a) is put in the incubator at 37 C., 

 the other (6) is kept at C. After an hour the two portions 

 are centrifugalized and the clear fluid from each is separated. 

 It is found that a small fraction of immune-body is present 

 in the fluid obtained from (a), this having dissociated at 



