592 FRAGMENTS OP 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 our 
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 coutagium. 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 tempevature, 
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 for inocula- 
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. 
