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. 



