70 BACTERIOLOGY. 



in small quantities under such precautions that it is 

 perhaps not contaminated, but ordinarily for laboratory 

 purposes a larger quantity is needed, so that the slaughter- 

 houses form the sources from which it is usually ob- 

 tained, and here a certain amount of contamination is 

 unavoidable, though its degree may be limited by proper 

 precaution. The animal from which the blood is to be 

 collected should be drawn up to the ceiling by the hind 

 legs, the head should be held well back, and with one 

 pass of a very sharp knife the throat should be com- 

 pletely cut through. The blood which will be spurting 

 from the severed vessels should be collected in large 

 glass jars which have been previously cleaned, disinfected, 

 and all traces of the disinfectant removed with alcohol 

 and finally ether. The latter evaporates very quickly 

 and leaves the jar quite dry. The jars should be pro- 

 vided 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 

 which can be tightly screwed down upon a rubber joint. 

 From two such jarfuls of blood one can recover quite 

 a large quantity of 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 



