INCUBATION OF CULTURES 



19 



be kept in the dark, as light is inimical to the development of 

 nearly all bacteria. 



Incubation at the body temperature presents more difficulty. 

 An incubator is almost essential when much work has to be done, 

 and of these Hearson's is by far the best. The smallest size costs 

 about £& los., and is a thoroughly reliable and durable affair. 

 Cheaper instruments are also procurable: the "Edinburgh" 

 incubator (Alex. Fraser, 22, Teviot Place, Edinburgh) costs about 



Fig. 10. — Incubator. 



£± I OS. complete. Foreign incubators can be obtained at an even 

 lower price, but are not very durable. 



Much can be done without the use of so expensive an apparatus 

 if the practitioner can find a room in which the temperature keeps 

 approximately constant throughout the twenty-four hours. A tin 

 biscuit box (or any other metal box) is covered with cotton-wool 

 on the top and sides, the bottom being left bare, and mounted on 

 a tripod stand. It is heated by means of an ordinary night-light 



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