A COMBAT WITH AN INFECTIVE ATMOSPHERE. 649 



I operated sometimes with tubes like those of Dr. Roberts, and some- 

 times with those which I call Cohn's tubes. These are formed by- 

 heating a certain portion of a test-tube and drawing it out so as to 

 leave an open funnel above, a bulb below, and a narrow tube between 

 both. These are Cohn's tubes. His method was this : He placed 

 the tubes, as they are placed here, in boiling water, and, when they 

 had been subjected to a boiling temperature for a sufficient time, he 



! 'I 



simply lifted them out. He found a certain amount of water con- 

 densed upon the neck of the bulb; he waited one or two minutes until 

 that evaporated, and then quietly plugged his tube with cotton-wool, 

 and he thought that this was perfect immunity against the entrance 

 of contamination; and Prof. Colm is very emphatic in saying that 

 there is no thought of contamination from without in pursuing this 

 method of experiment. I operated upon a great variety of hay-in- 

 fusions, and after a time, by pursuing with the most scrupulous exact- 

 ness the method laid down by Dr. Roberts and Prof. Cohn, it was 

 possible for me, by practice, now to corroborate and now to contra- 

 dict them. It is perfectly useless to bring forward before public as- 

 semblies merely opposing assertions, so that I did not really content 

 myself with falling back upon the results I obtained last year, but 

 tried to get some knowledge as to whence the differences arose which 

 showed themselves between me and these distinguished men. Here 



