

THERMAL DEATH-POINTS 63 
fluids in order to prevent all chance of their being 
“generating,” as well as “nourishing,” fluids. A 
clue in this direction had been met with two years 
previously, after dealing with the death-point in the 
saline solution, which is thus referred to! :—“ If, on 
the same slip, though under different cover-glasses, 
specimens of a hay infusion, turbid with Bacteria, 
are mounted (a) without being heated, (4) after the 
fluid has been raised to 122° F. for ten minutes, and 
(c) after the fluid has been heated to 140° F. for ten 
minutes, it will be found that in the course of a few 
days the Bacteria under a and 6 have notably in- 
creased in quantity; while those under ¢ do not 
become more numerous, however long the slip is 
kept.” Facts of a similar kind were also found at 
this period when a turnip infusion and an impure 
neutral saline fluid was dealt with. The multiplica- 
tion of Bacteria beneath the cover-glass, when 
it occurs, is soon rendered obvious even to the 
naked eye by the increasing cloudiness of the 
film. 
Under (c) there seemed to be clearly no origina- 
tion. Then, again, it was pointed out by Gruithuisen, 
early in the last century, that many infusions, other- 
wise productive, ceased to be so when they were 
poured into a glass vessel whilst boiling, and when 
this was filled, so that the tightly fitting stopper 
touched the fluid. Having myself proved the truth 
of this assertion, and ascertained that under such 
conditions infusions of hay and turnip acted only as 
“nourishing” fluids, the mode of experimentation 
1“ Modes of Origin of Lowest Organisms,” 1871, p. 60. 
