BLOOD-SERUM. 121 



The latter evaporates very quickly and leaves the jar 

 quite dry. The jars should be provided with covers, 

 which close hermetically ; these, too, should be care- 

 fully disinfected. The best form of vessels for the 

 purpose is the large 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 

 jarfuls of blood one can recover quite a large quan- 

 tity of clear serum, ordinarily from 500 to 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 may 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 exclude as much as possible of 



