202 THE FLOATING-MATTER OF THE AIR. 



example, may be more than three hours in London, and 

 less than three minutes at Kew.^ 



I will cite here two conspicuous illustrations of the 

 infective energy of those desiccated hay-germs in two 

 infusions which, under ordinary atmospheric conditions, 

 are very easily sterilized. On the 30th of March five 

 pipette-bulbs were charged with clear beef-infusion and 

 boiled for the following times : — 



1st bulb .... 



2nd „ . 



3rd „ ... 



4tli „ ... 



5tli „ . . . . 



After cooling, the sealed ends were broken off, the 

 air being admitted through cotton-wool plugs. Every 

 one of these bulbs became charged with organisms. In 

 the shed, eight yards off, this beef-infusion was, as 

 already reported, sterilized by five minutes' boiling. 



Precisely the same experiment was made on March 

 30 with pellucid mutton-infusion. Not one of the five 

 bulbs was sterilized. All of them are at this moment 

 charged with life. It behoves those engaged in the 

 industry of preserved meat and vegetables to keep clear 

 of the old-hay contamination. Probably they from 

 time to time have encountered difficulties and dis- 

 appointments which they could not explain, but which 

 may be solved by reference to the results here set forth. 



^ I have already described the distribution of BacteHa-gervas 

 in the air as ' Bacterial clouds.' Were our vision sufficiently 

 sharpened to see the manner in which such germs are distributed 

 ■over the surface of a meadow, we should not, I am persuaded, find 

 that distribution uniform. We should, in my opinion, find the 

 germs grouped in crowds, with comparatively free interspaces, like 

 violets on an alp, or mushrooms in a field. It is therefore con- 

 ceivable that two bunches of hay from the same meadow may 

 differ from each other in deportment. 



