A COMBAT WITH AN INFECTIVE ATMOSPHERE. 651 



not the slightest doubt that, if time permitted, I could heap up evi- 

 dence of this fact, that the wonderful sterility of this old hay is clue 

 to the induration and desiccation of the germs associated with it. 

 Here you have three tubes containing cucumber-infusion of crystalline 

 clearness ; they have been simply subjected to a boiling temperature 

 for ten minutes ; they have been completely sterilized, and they are 

 as clear as when the infusions were first introduced into the tubes. 

 On the other hand, here are tubes that have been subjected to a boil- 

 ing temperature for five hours and a half, showing a swarming de- 

 velopment of life. What is the reason of this difference ? The reason 

 depends entirely upon the method of experiment. When Dr. Roberts 

 filled his bulbs, he simply poured in his infusion, plugged his tube, 

 sealed it, and subjected it to a boiling temperature. Not only did 

 the liquid contain germs, there was a quantity of air above the liquid, 

 and the germs were diffused in the air. Germs thus diffused in the 

 air are very differently circumstanced from germs diffused in a liquid ; 



Fig. 3. 



they can withstand for hours a boiling temperature; whereas that 

 selfsame temperature, brought to bear upon germs immersed in liquid, 

 destroys them in a few minutes. And why do these tubes differ? 

 The reason is to be sought entirely in the method of filling the tubes 

 containing the clear infusions. Here is a diagram (Fig. 3), represent- 

 ing one of Dr. Roberts's bulbs. You see that the top is united to a 

 T-piece with a collar of India-rubber. This comes down and ends in 



