FIXATION OF COMPLEMENT 



105 



longer the time the more closely will they be packed. 

 From this it is easily seen that the method used of tak- 

 ing a definite amount of whole blood in the beginning 

 and from that calculating the dilution required is more 

 accurate than drawing out a quantity of the centri- 

 fuged corpuscles and making the dilution from them, 



Fig. 7. — Method of obtaining blood from sheep's ear. 



which is the method commonly employed. The clear 

 fluid above the corpuscles is poured off, and replaced 

 with normal salt solution, the tubes shaken, and again 

 centrifuged. This washing and centrifuging is re- 

 peated three or four times, in order to remove all 

 serum. If the corpuscle suspension is to be used in 

 the test itself, the fluid in each tube is finally brought 



