44 PROPERTIES OF ILEMOLYTIC SERA 



Another method is to determine whether R + IB molecules 

 saturated, say, for rabbit's complement are also saturated 

 for guinea-pig's complement. To one series (A) of tubes, 

 each containing the same amount of red corpuscles and the 

 same amount of IB, complement of rabbit is added in 

 increasing amounts, and the tubes are placed in the incubator 

 for two hours at 37 C. The same procedure is carried out in 

 another series (B), but at the end of the two hours a haemoly tic 

 dose of guinea-pig's C is added to each tube. The tubes of 

 both series are placed in the incubator for another hour, and 

 the presence of free C is tested for in the usual way. It is 

 evident that the first series will give the point of saturation 

 with rabbit's C, and the corresponding tube in the second 

 series will show whether such a tube can still take up guinea- 

 pig's complement. As an example, in one experiment it is 

 found that in series A the tube with 0-2 c.c. rabbit's C added 

 gives a fifth of a haemolytic dose of free C, whilst in series B 

 the tube containing 0-2 c.c. rabbit's C gives a full haemolytic 

 dose of free C. Thus it is shown that the tube saturated 

 with rabbit's C took up not more than a fifth of a dose of 

 guinea-pig's C. (A separate estimation carried out at the 

 same time gave 0-1 4 c.c. as the amount of guinea-pig's C 

 taken up by the same amount of red corpuscles treated with 

 IB.) It will be shown below that a corresponding result is 

 obtained by saturation with complementoids. 



We have, therefore, shown that in the case studied practically 

 all the molecules of the guinea-pig's complement combine with 

 the same E + IB molecules (sensitized receptors) of the ox as 

 the molecules of the rabbit's complement combine with. 



Another interesting point which presents itself is whether 

 the hsemolytic value of a complement corresponds with the 

 combining value. The heemolytic dose of normal rabbit's 

 serum in the case studied is always several times that of 

 guinea-pig's complement. This theoretically may be because 

 there are fewer complement molecules in a given amount of 



