254 COLLECTED STUDIES IN IMMUNITY. 



Here we see that the employment even of very high multiples of the 

 amboceptor effects a reduction in the amount of complement required 

 of one-third to one-sixth at the most. But what is particularly char- 

 acteristic for this case is the fact that the minimal amount of com- 

 plement is almost reached with a small multiple of the "amboceptor 

 unit," 1 and that it does not materially change with a further in- 

 crease of the amboceptor. Thus, in Table II, A, we see that when 

 five times the amboceptor unit is employed the amount of comple- 

 ment required is 0.01; when 25, 50, or 100 times the unit is employed 

 the complement is 0.008. Table II, B, shows that with the employ- 

 ment of two to three times the amboceptor unit the maximum of 

 complement action is already attained. 



An entirely analogous behavior is shown by the cases in Table III,, 

 in which the same blood and the same amboceptor are used as in 

 Table I, but in which different kinds of complement are added,, 

 namely, sheep serum and horse serum. 



These cases constitute the transition to those reproduced in Table 

 IV which deal with ox blood + the amboceptor of goats treated with 

 ox blood + three different complements, namely, guinea-pig, rabbit, 

 and sheep serum respectively. In these also a limit is reached beyond 

 which the decrease of complement required is but slightly or not at all 

 affected by an increase in the amount of amboceptor. 



We see therefore that with an increase of the amount of amboceptor 

 the amount of complement required at one time drops to a greater or less 

 degree, at another time it remains unchanged. Upon what does this 

 phenomenon depend? In order to explain this we must consider three 

 factors which may be combined with one another, and which must be 

 considered in each individual case. These are: 1. The receptors 

 present in the red blood-cell. 2. The conditions of affinity. 3. The 

 plurality of the amboceptors. 



So far as the first point is concerned we know that the amount of 

 receptors of the red blood-cells may exhibit great differences in any 

 individual case. 2 



1 We use the term " amboceptor unit" to specify that amount of amboceptor 

 which on the addition of the optimal amount of complement just suffices for com- 

 plete haemolysis. In the same sense R. Pfeiffer uses the term "immunity unit" 

 when speaking of bactericidal sera. Corresponding to the amboceptor unit 

 the "receptor unit" is that amount of receptor which binds the amboceptor 

 unit. 



2 See Ehrlich, Schlussbetrachtungen in Nothnagels spec. Pathologic und 

 Therapie, Vol. VIII, Vienna, Holder, 1901 ; and Ehrlich and Morgenroth, page 71. 



