146 THE FLOATING-MATTER OF THE AIR. 



the twenty-four tubes charged with infusion B had 

 become turbid, while sixteen of them remained perfectly 

 clear. I do not doubt that the tardy infection of some 

 of the tubes just referred to arose from external con- 

 tamination, which is almost inseparable from the method 

 of experiment. 



Here, while infusion A corroborated Professor 

 Cohn, infusion B in substance contradicted him, 



§ 5. Hay-infusions (in Closed Chambers). 



In dealing with hay-infusions I also fell back on the 

 method of experiment which was found so effectual in 

 1875,^ employing closed chambers in which the air had 

 been permitted to cleanse itself by the gradual subsi- 

 dence of its floating matter. 



On the 3rd of October, 1876, my experiments with 

 such chambers recommenced. Two of them, containing 

 each three large test-tubes, were then charged with an 

 infusion of hay accurately prepared according to the 

 prescription of Dr. Roberts. Its specific gravity was 

 1006 ; it was superneutralized to the proper extent with 

 caustic potash, but the period of boiling, instead of being 

 three hours, was five minutes. 



Examined from time to time for more than four 

 months subsequently, the infusion in both chambers 

 continued perfectly unchanged. It was free from sus- 

 pended matter, free also from every trace of scum, main- 

 taining for the light which passed through it a singular 

 transparency. 



Here, to a certainty, a period of boiling not amount- 

 ing to one-twentieth of that required by Dr. Eoberts, 

 sufficed to destroy totally the power of generating life 

 in an alkalized hay-infusion. 



* Briefly described in the Introduction. 



