of small quantities. After describing the principal appliances at
present in the market we propose to make some suggestions as to the
construction of larger apparatus.

A firm which has given great attention to the question of maintaining
fixed temperatures is that of Messrs. Charles Hearson & Co., Ltd. Their
incubators for chicken hatching are known all over the world; and their
appliances for biological incubation are very generally used in
bacteriological laboratories. With such experience it was natural that
they should turn their attention to soured milk apparatus, and the
result is the "Lactobator" (Figs. 50 and 51).

[Illustration: FIG. 50.--"Lactobator" made by Messrs.
Charles Hearson & Co., Limited, which is used for the
incubation of pure culture in milk in a fairly large way.
The illustration shows the "Lactobator" closed.]

[Illustration: FIG. 51.--Messrs. Hearson & Company's
"Lactobator," showing the internal arrangements.]

A copper vessel made to contain water has placed in it a stoneware jar
which holds two gallons of milk; on the top is a lid which carries a
thermometer for indicating the temperature of the milk. Heat is supplied
by a gas ring under the copper vessel; and in the gas supply is the
patent thermostat made use of by Messrs. Hearson also in their
biological and poultry incubators, in which a capsule containing a
liquid arranged to boil at a certain predetermined temperature is the
regulating factor. When the liquid boils, the capsule expands, and by
certain mechanical devices regulates the gas supply so as to produce
exactly the temperature required.

The procedure is as follows: The jar is filled with milk, and water is
run into the copper vessel by the funnel until it runs over at the
overflow pipe. The thermostat is lifted off and the full gas supply
allowed to pass to the burner, the temperature of the milk brought up to
180 deg. F. and maintained for half an hour at this figure. The gas is then
turned off, and cold water run through the funnel until the temperature
of the milk registers 95 deg. F. The culture is added, the lid replaced,
and the thermostat put into the pocket at the side of the vessel; the gas
relighted, and when the temperature reaches 100 deg. to 106 deg. F. the
capsule of the thermostat will expand and close the gas to a peep, which
is just sufficient to maintain the temperature within the above limits.
After eight hours the incubation is completed.