306 STUDIES IX [MMUNITY. 



This purification of the sensitizer is accomplished in our experi- 

 ments in which we have used corpuscles treated with their specific 

 serum.* If this precaution is neglected by mixing the whole 



immune serum, which contains other analogous substances in 

 addition to the specific sensitizer, with the antiserum in the first 

 place, the neutralizing effect is wasted. When we add to our 



sensitized corpuscles, either before or after mixing them with anti- 

 serum, normal sensitizers in the form of normal rabbit serum, 56 

 degrees (or indeed rabbit > ox serum deprived of its specific sen- 

 sitizer by contact with ox corpuscles) their cure is gravely com- 

 promised, since the neutralizing power of the antiserum ceases 

 to be concentrated on the sensitizer affecting the corpuscles. If, 

 therefore, the mixture is made in the usual manner, antiserum and 

 whole immune serum containing the specific sensitizer (or anti- 

 toxin or agglutinin, for these remarks are apparently applicable 

 to any of the antibodies) to be neutralized, the chance of obtaining 

 a neutralization depends on the relation of specific and normal sen- 

 sitizer content in the immune serum. The greater the relative amount 

 of normal sensitizers the less the specific sensitizer will be affected 

 by the antiserum, so that its neutralization may be practically nil. 

 And if the antisensitizers — or, one may say, the anti-antitoxins — 

 are found to be of relatively little potency or practically negative, 

 it is due at least in part to the fact that not all their activity is evi- 

 dent. When we expect to neutralize a given immune body in an 

 immune serum we do not consider that energy may be exhausted in 

 saturating other substances that are not taken into account in the 

 experiment and of the presence which we may actually be ignorant. 

 It would be strange, indeed, that the relative proportion of normal 

 and specific sensitizers should be the same in all immune sera from 

 no matter w T hat animal species. It must be expected, then, that 



* It would be desirable, to be sure, to obtain pure sensitizer in some other way. 

 It would then be possible to treat it with antiserum before it was united with the 

 blood cells. Hitherto such a separation has not been possible, although it would 

 be theoretically better than the method we have employed. It is indeed possible 

 that the antisensitizer should show no preventive action on pure sensitizer, 

 although it can cure sensitized corpuscles. It would seem, indeed, from our 

 experiments that there is some struggle between the affinity of the sensitizer for 

 the corpuscle on the one hand, and for the antisensitizer on the other. And it 

 may be that in certain cases the combination between sensitizer and corpuscle 

 may be so stable as to prevent any curative action by an antiserum. 



