PROPERTIES OF COMPLEMENTOIDS 65 



tioned there is still free complement in the medium of 

 suspension. We take two series (A and B) of tubes each 

 containing O5c.c. of suspension of red corpuscles along 

 with five doses of IB ; the medium in A being salt solution, 

 in B guinea-pig's serum heated at 55 C. To the several 

 tubes in the two series increasing doses of complement are 

 added. After lysis is complete in the tubes of series A 

 we test as to the comparative amount of free complement 

 in the two series. The fluid from each tube of series A is 

 added to another tube containing 0-5 c.c. of guinea-pig's 

 serum 55, the fluid obtained by centrifugalization from 

 each tube of series B is added to a tube containing 0-5 c.c. 

 of salt solution (0-85 per cent.). In this way any free com- 

 plement obtained from the tubes of either series is now 

 in a mixture of equal parts of heated serum and salt solution. 

 To each tube we now add the corpuscles of 0-5 c.c. of suspen- 

 sion treated with immune-body and the tubes are placed 

 in the incubator. It is found that lysis takes place much 

 more readily in the tubes containing the fluid from series B, 

 i.e. there was much more free complement in this series. 

 Such an experiment is complementary to and confirmatory 

 of the result recorded above. 



Having thus seen that the combination of complement 

 with corpuscles treated with immune-body is interfered with 

 when guinea-pig's serum 65 is the medium of suspension, 

 we have to inquire how this is brought about. 



Now it is to be noted that the guinea-pig's complement 

 (normal serum) is much the most active of the complements 

 used, and that this serum when heated interferes with 

 haemolysis more than the others. In a preceding section 1 

 we have given reasons for believing that there are more 

 complement molecules in the guinea-pig's serum than (for 

 example) in the same quantity of rabbit's serum. We 

 have also given methods for demonstrating by test-tube 



1 Vide p. 45. 



MT7IR T? 



