FIXATION OF COMPLEMENT 109 



pig is etherized by placing its head in a glass contain- 

 ing gauze soaked with ether, and before death occurs, 

 the blood-vessels of the neck are severed and the blood 

 collected in a Petri dish (Fig. 9) . More blood will be 

 obtained if drawn before respiratory and cardiac 

 movements cease, and from 10 to 15 c.c. should be col- 

 lected in this manner. The blood is allowed to coagu- 

 late, and the clear serum to separate, which it does in 

 about two hours. The serum is then drawn off with a 

 capillary pipette and diluted in the proportion of one 

 part in ten with 0.85 per cent, salt solution, i.e., to 1 

 part of serum 9 parts of salt solution are added. The 

 complemental property of serum is soon lost, and the 

 guinea-pig serum should therefore be used on the day 

 it is obtained, or not later than the following day, if 

 kept on ice over night. 



The different reagents having been prepared as 

 above described, we are now ready for the titration. 

 The rabbit's serum, after having been inactivated, is 

 made up in the following dilutions: 1-500, 1-1000, 

 1-1500, 1-2000, 1-3000, 1-4000, and 1-5000, in nor- 

 mal salt solution. In a series of test-tubes 1 c.c. of 

 each of these dilutions is placed, together with 1 c.c. of 

 a 5 per cent, suspension of sheep's corpuscles and 0.1 

 c.c. of the 1-10 dilution of guinea-pig complement, 

 with sufficient salt solution to bring the total volume 

 up to 4 c.c. After their contents have been thoroughly 



