1907.] Complement-content of Fresh Blood-serum. 383 



shown by Mainwaring (4) to be open to serious objections. On the other 

 hand, we cannot simply ignore the immune-body contained in the serum. 

 By taking varying doses of the serum we should be taking not only varying 

 quantities of complement, but also varying quantities of immune-body ; and 

 Morgenroth and Sachs (5) have shown that the amount of complement 

 necessary for haemolysis depends in some measure on the amount of immune- 

 body present. Now, in the process of immunising, the animal responds by 

 a great increase of immune-body in its serum, but there is no corresponding 

 increase of complement. Of the serum of a highly immunised animal, 

 therefore, it is possible to find a dose which contains enough immune-body to 

 cause total laking of the chosen quantity of corpuscles, but does not contain 

 enough complement. Complete haemolysis, therefore, does not occur with 

 that dose, unless we make good the lack of complement by adding some from 

 another source. By making use of this fact, a method was devised of 

 estimating the complement in immune serum. An immunised animal was 

 bled and samples of serum were withdrawn from the clot in the usual way, 

 each sample being tested at once after centrifuging. Such a dose as has been 

 just described, containing enough immune-body but not enough complement, 

 was taken, and the same dose was taken for all the samples. Since, as we 

 have just seen, the immune-body does not vary in the different samples, we 

 are thus taking always the same amount of immune-body. The deficiency 

 in complement was supplied by adding the serum of a normal rabbit, and the 

 quantity of this serum which had to be added was carefully determined for 

 each sample. The greater the quantity of normal serum required, the less 

 complement must the dose of immune serum contain. The amount of 

 normal serum that would be required, if the dose of immune serum 

 contained no complement, is readily found by first heating the latter and so 

 destroying its contained complement. The difference between this amount 

 and the amount we had to add when the sample was unheated gives us 

 a measure of the value of the complement contained in the unheated dose, 

 this value being expressed in terms of the normal serum. We can thus 

 determine the amount of complement contained in each sample, and so 

 ascertain the extent of the variation, if any. 



Example 5. — Four cubic centimetres of 1-per-cent. suspension of ox 

 corpuscles ; 2 hours at 37° C. Immune serum from rabbit, injected 

 with ox corpuscles; of this serum, when heated, 0*02 c.c. required the 

 addition of 0*25 c.c. normal rabbit serum (i.e., complement) to produce total 

 haemolysis, and this quantity of the normal serum by itself produced no 

 lysis. 



2 F 2 



