54 JOURNAL OF SCIENCE. 
Numerous experiments have been devised to find out whether 
putrefaction is invariably due to these floating germs contained 
in the air, or whether Bacteria may not sometimes be formed by 
spontaneous generation. | The aim of all the experiments is the 
same—to destroy all living matter present in the fluid, by expos- 
ing it to sufficient heat, and then to fasten it up in such a way 
that no germs can possibly enter it from without. If these two 
conditions are properly fulfilled, any developement of life which 
may occur must be due to spontaneous generation. Unfortu- 
nately it is not always easy to carry out these conditions with ab- 
solute certainty. I will now describe some of the chief methods 
which have been devised with a view of meeting the case. 
1. The fluid is placed ina glass tube or small flask with a 
long drawn-out neck; heat is applied and the fluid boiled 
thoroughly ; then while steam is freely issuing from the neck, a 
second flame is brought in contact with the latter so as to melt 
the glass and thoroughly close the aperture. By this method 
the space above the fluid is a vacuum. | 
2. The fluid is placed ina flask'connected by a metal stop- 
cock with a metal tube placed in a small furnace. The fluid is 
boiled and at the same time the tube is heated to redness ; then 
the liquid is allowed to cool, the tube being still red-hot. As the 
steam in the flask condenses its place is taken by air which has 
all passed through the red-hot tube and may therefore be sup- 
posed to have had all its germs destroyed. When the flask is 
cold, the stopcock is turned, and the flask detached from the 
tube. ; 
3. The fluid is boiled in a flask and while ebullition is going 
on the neck of the flask is thoroughly plugged with cotton wool. 
In this case all the air entering the flask is filtered in passing the 
cotton wool, and so freed from germs. 
4. A very ingenious method was devised by Prof. Tyndall in 
which the fluid could be freely exposed to the air and yet the 
entrance of germs prevented. 
The apparatus* by which this is effected consists of a wooden 
box, with a glass front, and with a small glass window in each 
of two opposite sides. Into the bottom are fixed, air-tight, a 
number of test-tubes ; into the top are similarly fixed two glass 
tubes bent into zig-zags, and forming a free communication 
between the interior of the box and the outside air; a long glass 
funnel passes through a stuffing box at the top of the case, and is 
so arranged that its lower end can be brought over all the test- 
tubes in succession. The apparatus is supported on strong legs, 
and the whole of its interior—including that of the bent tubes— 
is smeared with glycerine. 
(To be continued.) 
* Figures and full descriptions of this apparatus will be found in Tyndall’s 
‘Floating Matter of the Air,” a book which everyone interested in these questions 
should read, 
