128 Manual of Veterinary Microbiology. 



times in succession one species will be obtained in a 

 pure state. 



Cohn has separated certain germs by taking advan- 

 tage of the resistance of their spores to a few mo- 

 ments ebullition. The bacillus subtilis, or hay bacil- 

 lus, is obtained by boiling neutral infusion of hay and 

 then transferring to the incubator. The spores of 

 the bacillus subtilis alone develop because these alone 

 have resisted. 



Germs can be isolated by more direct means. 



31ethod of isolatioii by Salmonsen's capillary tube. — 

 This author has studied, in this way, the various 

 germs which grow in putrefactive blood. He aspirated 

 defibrinated blood into long capillary tubes which he 

 closed at both ends and fixed upon a horizontal card. 

 The few germs which are included in the tube grow 

 separately in the different parts of its length ; their 

 evolution can thus be studied and the}'' can be col- 

 lected separately for cultivation. 



3Iethod of isolation by dilution. — A material, rich in 

 germs of different kinds, is diluted with sterilized 

 water so that the germs are considerably rarefied. 

 This liquid is then inoculated by drops into a series 

 of culture vessels ; those of these vessels which have 

 received only one germ will give a pure culture on 

 incubation. 



MM. Roux and Yersin have succeeded in isolating 

 the bacillus of human diphtheria by making with a 

 platinum wire charged with a trace of false mem- 

 brane, longitudinal streaks in a series of tubes of 

 blood serum. The germs become progressively rare- 

 fied on the wire and ultimately the serum in the last 



