1904] 



Combining Properties of Serum- Complements, etc. 



13 



of C and Cd in equal parts. If the C and Cd molecules have the same 

 combining power, it is evident that the saturation of the R + IB 

 molecules will occur after the addition of the same amounts in the two 

 cases. After the saturation point has been reached, however, twice 

 as much of the C + Cd mixture as of the undiluted C would have to be 

 added before a free dose of C would be obtained. As a matter of 

 fact, this is pretty much what happens. 



The following may be taken as examples : 



I. Two series of tubes, A and B, 3D of IB added to each tube, and 

 lysis is produced in all by ID of C = O05 c.c. C is then added in 

 increasing amounts. 



A. 



II. 5D of IB to each tube. M.H.D. of C = 0-03. 



A. 



It appears from these examples that the points at which free C 

 appears in the two cases ( (a), where pure C is used, and (b) where a 

 mixture of C and Cd in equal parts is used) approximately correspond 

 only a little more of the mixture of C and Cd has to be added before 

 saturation of the E + IB molecules occurs. It is also seen that, after 

 the saturation point has been reached, fully twice as much of the 



