234 



FIXATION OF THE COMPLEMENT 



3. Sterile normal saline solution. The volume of fluid in each tube used in 

 the test should, if the experiment is to be conclusive, be the same. After 

 the various ingredients have been added sufficient nor- 

 mal saline solution is poured in to bring the volume up 

 to, generally, 2 c.c. 



Red cells. Sheep or rabbit red cells are generally 

 used. They must be separated and washed in the manner 

 already described (p. 230). 



After the third washing prepare a 5 per cent, solution 

 of the cells in normal saline solution. 



Haemolytic serum. The method of preparing haemo- 

 lytic serums has been described above (p. 230). If 

 sheep cells are used as the indicator the serum of a 

 rabbit inoculated with sheep cells is employed, and 

 for rabbit cells the serum of a guinea-pig inoculated with 

 rabbit cells. 



After collecting the blood in the ordinary way (Chap. 

 XII.) the serum is decanted and then inactivated by 

 heating for half an hour at 55 C. in sealed ampoules. 

 The hsemolytic serum should be stored in an ice chest 

 and it will then retain its heemolytic properties for 

 several months. 



It is absolutely necessary to titrate the haemolytic 

 serum. This can be done in the manner indicated in 

 the following table. In a series of tubes prepare the 

 mixtures shown in the horizontal lines, incubate at 37 C. for 15-30 minutes 

 and note the results. 



