BLOOD-SERUM. 95 



isms commonly found in the ground, the spores of which 

 are among the most resistant known. The so-called 

 " potato bacillus" is one of this group; it is an organ- 

 ism which is not infrequently more or less of an obstacle 

 to the work of the beginner. 



Blood-serum. — Originally blood-serum required 

 special care in its preparation; it was always necessarj' 

 to reduce the unavoidable contamination, which to a 

 certain extent occurs when the blood is obtained, to the 

 minimum degree. 



It is possible to collect serum from small animals and 

 in small quantities under such precautions that it is per- 

 haps not contaminated; but, ordinarily, for laboratory 

 purposes a larger quantity is needed, so that the 

 slaughter-houses form the source from which it is usu- 

 ally obtained, and here a certain amount of contamina- 

 tion is unavoidable, though its degree may be limited 

 by proper precaution. 



The steps that were formerly thought to be essential 

 to the successful collection of blood and the preparation 

 of serum for culture purposes were about as follows : 



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 completely cut 

 through. The blood which spurts 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 provided with 

 covers which close hermetically — these, too, should be 

 carefully disinfected. The best form of glass vessels 



