316 THE FLOATING-MATTER OF THE AIR. 



brief exposure to a temperature between 140° and 150° 

 Fahr. This may be regarded as the death-point of the 

 lymph, or rather of the particles diffused in the lymph, 

 which constitute the real contagium. If no time, how- 

 ever, be named for the application of the heat, the term 

 ' death-point ' is a vague one. An infusion, for example, 

 which will resist five hours' continuous exposure to the 

 boiling temperature, will succumb to five days' exposure 

 to a temperature 50° Fahr. below that of boiling. The 

 fully developed soft bacteria of putrefying liquids are 

 not only killed by five minutes' boiling, but by less 

 than a single minute's boiling — indeed, they are slain 

 at about the same temperature as the vaccine. The 

 same is true of the plastic, active bacteria of the turnip 

 infusion.' 



But, instead of choosing a putrefying liquid for 

 inoculation, let us prepare and employ our inoculating 

 substance in the following simple way : — ^Let a small 

 wisp of hay, desiccated by age, be washed in a glass of 

 water, and let a perfectly sterilized turnip infusion be 

 inoculated with the washing liquid. After three hours' 

 continuous boiling the infusion thus infected will often 

 develope luxuriant bacterial life. Precisely the same 

 occurs if a turnip infusion be prepared in an atmosphere 

 well charged with desiccated hay-germs. The infusion 

 in this case infects itself without special inoculation, 

 and its subsequent resistance to sterilization is often 

 very great. On the 1 st of March last I purposely in- 

 fected the air of our laboratory with the germinal dust 

 of a sapless kind of hay mown in 1875. Ten groups 



' In my paper in the Philosophical Transactions for 1876, I 

 pointed out and illustrated experimentally the difference, as regards 

 rapidity of development, between water-germs and air-germs ; the 

 growth from the already softened water-germs proving to be prac- 

 tically as rapid as from developed bacteria. This preparedness of 

 the germ for rapid development is associated with its preparedness 

 for ranid destruction. 



