346 FRAGMENTS OF SCIENCE 



them escapes destruction. The same is true of the turnip 

 infusion if it be inoculated with the living bacteria only 

 — the aerial dust being carefully excluded. In both cases 

 the dead organisms sink to the bottom of the liquid, and 

 without reinoculation no fresh organisms will arise. But 

 the case is entirely different when we inoculate our tur- 

 nip 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°, and do not survive a tem- 

 perature of 150°, the death- point lies somewhere between 

 these two temperatures. Yaccine lymph, for example, is 

 proved by Messrs. Braidwood and Vacher to be deprived 

 of its power of infection by brief exposure to a tempera- 

 ture 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 conta- 

 gium. 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' con- 

 tinuous 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 — in- 

 deed, they are slain at about the same temperature as the 

 vaccine. The same is true of the plastic, active bacteria 

 of the turnip infusion.* 



* In my paper in the "Philosophical Transactions" for 18 V6, I pointed out 

 and illustrated experimentally the difference, as regards rapidity of development. 



