592 FRAGMENTS OF SCIENCE. 



dead organisms sink to the bottom of the liquid, and 

 without re- inoculation no fresh organisms will arise. 

 But the case is entirely different when we inoculate oui 

 turnip infusion with the desiccated germinal matter afloat 

 in the air. 



The " death-point" of bacteria is the maximum tem- 

 perature at which they can live, or the minimum tempera- 

 ture at which they cease to live. If, for example they 

 survive a temperature of 140 degrees, and do not survive a 

 temperature of 150 degrees, the death-point lies somewhere 

 between these two temperatures. Vaccine lymph, for 

 example, is proved by Messrs. Braid wood and Vacher to 

 be deprived of its power of infection by brief exposure to a 

 temperature between 140 and 150 degrees Fahr. This 

 may be regarded as the death-point of the lymph, or 

 rather of the particles diffused in the lymph, which con- 

 stitute the real contagium. If no time, however, 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 

 degrees 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 temper- 

 ature as the vaccine. The same is true of the plastic, 

 active bacteria of the turnip infusion.* 



But, instead of choosing a putrefying liquid formocula- 

 tion, 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 bacte- 

 rial life. Precisely the same occurs if a turnip infusion be 

 prepared in an atmosphere well charged with desiccated 



*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 practi- 

 cally as rapid as from developed bacteria. This preparedness of the 

 germ for rapid development is associated with its preparedness for 

 rapid destruction. 



