BLOOD-SERUM. 87 



The jars should be provided with covers which close 

 hermetically — these too should be carefully disinfected. 

 The best form of glass vessels for the purpose are the 

 large glass museum jars of about one gallon capacity, 

 which close 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 quantity 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 adhesions to 

 the wall of the jar that might have formed, and which 

 would prevent the sinking of the clot to the bottom. 

 The covers are then tightly replaced, and with as little 

 agitation as possible 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 organisms 

 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 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 



