112 



BAaTEBIOLOGY. 



the coloring-matter of the blood, it may be placed again 

 in the ice-chest for twenty-four hours, during which 

 time the corpuscular elements will sink to the bottom, 

 leaving the supernatant fluid quite clear. This may 

 then be pipetted off, either into sterilized test-tubes, 

 about 8 c.c. to each tube, or into small sterilized flasks 

 of about 100 c.c. capacity. It is then to be sterilized 

 by the intermittent method at low temperatures, viz., for 

 one hour on each of five consecutive days at a tempera- 

 ture of 68°-70° C. During the intervening days it is 

 to be kept at the room-temperature to permit of the 

 development of any spores that may be present into 

 their vegetative forms, in which condition they are 

 killed by an hour's exposure to the temperature of 

 70° C. 



Fig. 19. 



Chamber for sterilizing and solidifying blood-serum. (Koch.) 



At the end of this time the serum in the tubes may 

 either be retained as fluid serum or solidified at between 



