SPONTANEOUS GENERATION. 601 



which they can live, or the minimum temperature at which they 

 cease to live. If, for example, they survive a temperature of 140, 

 and do not survive a temperature of 150, the death-point lies some- 

 where 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 consti- 

 tute the real contagium. If no time, however, be named for the ap- 

 plication 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 below that of boiling. The fully-developed, soft bac- 

 teria 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. 1 But, instead of choos- 

 ing 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 

 develop 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 1st of March last I purposely infected the air of our 

 laboratory with the germinal dust of a sapless kind of hay mown in 

 1875. Ten groups of flasks were charged with turnip infusion pre- 

 pared in the infected laboratory, and were afterward subjected to the 

 boiling temperature for periods varying from 15 minutes to 240 min- 

 utes. Out of the ten groups only one was sterilized that, namely, 

 which had been boiled for four hours. Every flask of the nine groups 

 which had been boiled for 15, 30, 45, 60, 75, 90, 105, 120, and 180 

 minutes respectively, bred organisms afterward. The same is true 

 of other vegetable infusions. On the 28th of February last, for ex- 

 ample, I boiled six flasks, containing cucumber-infusion prepared in 

 an infected atmosphere, for periods of 15, 30, 45, 60, 120, and 180 

 minutes. Every flask of the group subsequently developed organisms. 

 On the same day, in the case of three flasks, the boiling was prolonged 

 to 240, 300, and 360 minutes ; and these three flasks were completely 



1 In my paper in the "Philosophical Transactions" for 1876, I pointed out and illus- 

 trated 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 

 practically as rapid as from developed bacteria. This preparedness of the germ for rapid 

 development is associated with its preparedness for rapid destruction. 



