DE. W. EOBEETS ON BIOGENESIS. 
459 
filled with beef-tea or a decoction of turnip, as represented in fig. 1. A plug of cotton- 
wool is also inserted into the upper end of the glass tube at a. ihe flask is then boiled 
over the flame for five minutes. When the flask is quite cold, Fig. 1. 
the plug at a is gently withdrawn. The liquid in a flask thus 
prepared remains permanently barren. In a week or two the 
condensed steam collected at the bend of the tube dries up, and 
the tube becomes an open channel into the flask. If the flask be 
examined at the end of two or three months, the contained liquid 
will be found still perfectly transparent. The experiment may 
then be carried a step further. If the little tube (a b ) be pressed 
downward through the cotton-wool plug until the U-shaped portion 
is completely submerged, as represented by the dotted lines in the 
figure, the liquid in the flask is brought into contact with the 
particles of air-dust collected in the bend of the tube. The result 
of this contact is speedily seen ; for in a few days patches of 
mould appear on the surface, or the liquid becomes turbid from 
Bacteria *. 
These experiments admit of an easy explanation on the pan- 
spermic theory. The living germs and organisms contained within 
the flasks are killed by the heat during ebullition ; and the fresh supplies of air which 
enter the flasks on cooling are deprived of their germs — in the first case by filtration 
through the cotton-wool plug ; in the second case they are arrested in the bend of the 
tube a b, the shorter limb of which they are unable to ascend against the force of 
gravity ; and thus the necrosis at first effected by the heat is succeeded by a state of 
permanent sterility through want of living germs to start the process of germination. 
The condition of “ permanent sterility ” here described is essentially characterized 
by loss of the power of originating organisms with conservation of the power of 
nourishing and promoting the growth of organisms. 
The degree of heat required to induce this state of permanent sterility varies greatly 
according to the nature of the materials operated upon. 
Pasteur long ago pointed out that milk required more heat to sterilize it than 
sweetened yeast-water ; more recently Dr. Bastian and others have shown that turnip- 
infusion with cheese and some other mixtures cannot be sterilized, as an ordinary 
decoction can, by boiling for five or ten minutes; and experiments to be presently 
Bent-tube experiment 
simplified. 
* The barrenness in these experiments is not so absolutely permanent as in the simple plugged-flask experi- 
ment, as may be seen from the following observation : — On June 1 9th, 1872, I put up a flask of beef-tea in 
the manner above described, but in the process of boiling some of the beef-tea frothed over into the bend of 
the tube. On March 27th, 1873, the liquid in the flask was still quite unaltered, but I could see minute specks 
of mould creeping up the short limb of the tube a b, and about to drop into the liquid below. A few days after 
specks of mould began to appear on the surface of the liquid in the flask ; these speedily grew until they covered 
the entire surface. 
3 p 2 
