BLOOD-SERUM. 



97 



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 

 76°-80° C. In solidifying the serum the tubes should 

 be placed in an inclined position so that as great a sur- 

 face as possible may be given to the serum. The pro- 

 cess of solidification requires constant attention if good 



