BLOOD-SERUM. 71 



hours. The temperature should, however, not be low 

 enough to prevent coagulation, but should be sufficiently 

 low to interfere with the development of any living or- 

 ganisms that may be present. The temperature of the 

 ordinary domestic refrigerator is sufficient for the purpose. 

 After twenty-four to forty- eight hours the clot will have 

 become firm, and will be seen at the bottom of the jar. 

 Above it is a quantity of dark straw-colored serum. 

 The serum may then be drawn off with a sterilized 

 pipette and placed in tall cylinders which have previ- 

 ously been plugged with cotton wadding and sterilized. 

 After treating all the serum in this way, care having 

 been taken to get as little of the coloring matter of the 

 blood as possible, 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 inter- 

 mittent method at low temperatures, viz., for one hour on 

 each of five consecutive days at a temperature 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. 



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 surface as possible may be given to the serum. The 

 process of solidification requires constant attention if 



