VITAXITY OF PUTEEFACTIVE ORGANISMS. 177 



more conclusive than it -would have been had all three 

 tubes remained intact ; for had the power of developing 

 the organisms which produced the turbidity been in- 

 herent in the infusions, its action would not have been 

 confined to a single tube. 



It will be understood that when the chamber is 

 lifted from the oil-bath in which its infusions are boiled, 

 the air within the chamber contracts, and an indraught 

 is the consequence. If the entering air be properly 

 sifted, by passing it through cotton-wool plugs, no harm 

 is done ; but if it enter an aperture imsifted, it carries 

 its motes along with it. In the beef-chamber just re- 

 ferred to an aperture of this kind, about the size of a 

 pin-hole, was detected. This obviously was the door 

 through which the contagium entered. Through a 

 similar but graver defect in its chamber the sole- 

 infusion also broke down ; but in a subsequent experi- 

 ment with sole-infusion in the Jodrell laboratory, two- 

 thirds of the whole number of tubes charged with it 

 remained free from all trace of life. 



§ 15. Experiments on the Roof of the 

 Royal Institution. 



With a view to making, nearer home, experiments 

 similar to those made at Kew, I had a wooden shed 

 erected on the roof of our laboratory. The shed was 

 provided with benches, water and gas-pipes, and a stove 

 for heating. To an infusion of cucumber, which I had 

 found extremely intractable in the laboratory, my atten- 

 tion was first directed. Two tin chambers of three 

 tubes each were prepared, and transferred to the shed 

 fiom the workshop where they were made, without 



