PROPERTIES OF COMPLEMENTS 43 



combination to take place for an hour at 37 C., and then 

 test as before how much guinea-pig's C will be taken up, 

 (It is convenient in such experiments to produce lysis first 

 in all the tubes, in a case such as the present by guinea- 

 pig's C. The amount of C used for initial lysis, of course, is- 

 added to the final result.) The excess in the amount of 

 guinea-pig's C taken up in series A over that taken up in 

 series B gives the amount which has been kept out by the 

 amount of rabbit's C used. The following may be cited as 

 examples : 



1. No. 3. M.H.D. of guinea-pig's C = 0-05 c.c. ; M.H.D. of 

 rabbit's C = 0-22 c.c. About 3 D of IB added to each of two series 

 of tubes, each tube containing 1 c.c. suspension of red corpuscles. 



Series A. Guinea-pig's C alone added. Amount taken up = 

 0-24 c.c. 



Series B. 0-25 c.c. rabbit's C first, and then guinea-pig's C. 

 Amount of guinea-pig's C taken up = 0-19 c.c. 



Therefore, 0-25 c.c. of rabbit's C has kept from combination about 

 0-05 c.c. guinea-pig's C. 



2. No. 24. M.H.D. of guinea-pig's C = 0-04 c.c. ; M.H.D. of 

 rabbit's C = 0-3 c.c. About 3 D of IB added to each tube as before. 



Series A. Rabbit's C alone added ; amount taken up = 1-35 c.c. 



Series B. 0-04 c.c. of guinea-pig's C first, and then rabbit's C. 

 Amount of rabbit's C taken up = 0-9 c.c. 



Therefore, 0-04 c.c. of guinea-pig's C has kept out 045 c.c. 

 rabbit's C. 



3. No. 31. M.H.D. of guinea-pig's C = 0-0175 c.c. ; M.H.D. of 

 rabbit's = 0-1 c.c., 4 D of IB added to each tube. 



Series A. Guinea-pig's C alone added. Amount taken up = 

 0-11 c.c. 



Series B. 0-1 c.c. of rabbit's C first, and then guinea-pig's C, 

 Amount of guinea-pig's C taken up = 0-09 c.c. 



Therefore, 0-1 c.c. rabbit's C has kept out 0-02 c.c. guinea-pig's C, 



In all our experiments, of which the three cited are only 

 examples, the result has been the same guinea-pig's com- 

 plement keeps out rabbit's complement and conversely 

 rabbit's complement keeps out guinea-pig's. 



