126 Milk and Its Products 
day, so as to check carelessness in any place, and 
materially reduce the chances for contamination. 
The outline of methods and apparatus given here- 
with will enable anyone with a little skill and inge- 
nuity to make bacterial determinations sufficiently 
accurate for purposes of control in the production of 
high-grade milk. 
The laboratory.—In fitting out a small laboratory 
for the determination of bacteria in milk, much can 
be left to the ingenuity of the individual. It is neces- 
sary to have the work done in a place as free from 
‘dust and other contamination as possible. So, if the 
room has to be used also for other purposes, it is well 
to shut off or enclose with glass a small portion to be 
used for this work alone, and in which the sterile 
glassware, media and water may be kept, so that 
everything is ready and convenient for use at any time. 
Apparatus.—In choosing a sterilizer for glassware, 
any kind of an oven fitted with a thermometer, and 
in which a temperature of 150° C. can be maintained, 
will do. For sterilizing media and water, an auto- 
clave, that is, a steam sterilizer which is able to main- 
tain a pressure of at least ten pounds per square inch, 
is most convenient; there are also on the market 
“high altitude” or Denver cookers that are satisfactory. 
If neither of these is available, steamers or simply 
boiling water may be used. It must be remembered, 
however, that, unless pressure is used, a greater period 
of heat is necessary, and that with substances such as 
gelatin and milk, which will not stand such treatment, 
the intermittent method of sterilization must be used. 
