96 BACTERIOLOGY. 



for the purpose is the large glass museum jar of about 

 one gallon capacity, which closes by a cover that can be 

 tightly screwed down upon a rubber joint. From two 

 such jarf uls of blood one can recover quite a large quan- 

 tity of clear serum, ordinarily from 500-700 c.c. The 

 jars having been filled with blood, their covers are placed 

 loosely upon them and they are allowed to stand for 

 about fifteen minutes until clotting has begun. At the 

 end of this time a clean glass rod is passed around the 

 edges of the surface of the clot to break up any adhe- 

 sions to the side of the jar that might have formed, and 

 which would prevent the sinking of the clot to the 

 bottom. The covers are then replaced and tightly 

 clamped in position, and with as little agitation as pos- 

 sible the jars are placed in an ice-chest, where they 

 remain for twenty-four to forty-eight 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 organ- 

 isms 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 

 that have previously 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 



