BLOOD-SERUM. 91 



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 necessary 

 to reduce the unavoidable contamination, which to a 

 certain extent occurs when the blood is obtained, to its 

 minimum degree. 



It is possible to collect serum from small animals and 

 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 obtained, and here a certain amount of contam- 

 ination 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 re- 

 moved with alcohol and, finally, ether. The latter evap- 

 orates very quickly and leaves the jar quite dry. The 

 jars should be provided with covers which close her- 

 metically these, too, should be carefully disinfected. 

 The best form of glass vessels for the purpose is the 



