162 THE FLOATING-MATTER OF THE AIR. 



On the 30th of November all the infusions were 

 thickly turbid throughout and heavily coated with scum. 



From some of the precautions already mentioned it 

 may be inferred that before this point of the inquiry 

 had been reached, I had begun to suspect the atmo- 

 sphere in which I worked. Hay of various kinds, both 

 old and new, had been exposed and shaken about in the 

 laboratory, the air of which doubtless contained multi- 

 tudes of spores which diffused and insinuated themselves 

 everywhere. So, at all events, I reasoned. On the 

 20th of November, therefore, I had infusions of cucum- 

 ber, beetroot, parsnep, and turnip prepared, far from the 

 laboratory, in one of the highest rooms of the Eoyal 

 Institution, and introduced into four new chambers of 

 three tubes each. I deemed the precaution of prepar- 

 ing the infusions and introducing them in the distant 

 room sufficient. Accordingly, when the chambers were 

 charged they were carried down, and the infusions boiled 

 in the laboratory. 



Two days afterwards the parsnep alone remained clear. 

 This, however, was only a respite, for a day or two sub- 

 sequently it fell into the condition of its neighbours. 

 On the 30th of November both turnip- and parsnep- 

 infusions were turbid throughout, and laden at the 

 surface with thick fatty scum. The cucumber was also 

 heavily laden with scum, which sent long streamer-like 

 filaments into the subjacent liquid. The beetroot agreed 

 with the others in becoming turbid, but differed from 

 them in remaining free from scum. In no case last year 

 did turnip-infusion show the deportment here described. 

 Knowing, then, .from multiplied experiments, that turnip 

 possessed no inherent power of life-development, the 

 conclusion was irresistible that its present behaviour, 

 and with it the behaviour of cucumber, beetroot, and 

 parsnep, were due to infection from without. 



