SPONTANEOUS GENERATION. 329 



survive a temperature of 150, the death-point lies 

 somewhere between -these two temperatures. Vaccine 

 lymph, for example, is proved by Messrs. Braidwood 

 and Vacher to be deprived of its power of infection by 

 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 ex- 

 ample, which will resist five hours' continuous exposure 

 to the boiling temperature, will succumb to five days' 

 exposure to a temperature of 50 Fahr. below that of 

 boiling. The fully developed soft bacteria of putrefy- 

 ing 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 sterilised 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 my paper in the 'Philosophical Transactions' for 1876, 1 

 pointed out and illustrated experimentally the difference, as re- 

 gards rapidity of development, between water-germs and air- 

 germs; the growth from the already softened water-germs prov- 

 ing to be practically as rapid as from developed bacteria. This 

 preparedness of the germ for rapid development is associated 

 with its preparedness for rapid destruction. 



