26 BACTERIOLOGICAL DIAGNOSIS. 



and remains constant for long periods whatever be the 

 external temperature. It is hardly necessary for the 

 practitioner to purchase one of these. Careful search 

 in the house will usually reveal some cupboard or 



FIG. io. Incubator. 



corner in which the temperature will remain sufficiently 

 near 20 C. for a sufficiently long period; it is more 

 important that it should not rise above 22 C. than that 

 it should not fall below 18 C., as the former tempera- 



