1 8 CLINICAL BACTERIOLOGY AND H^MATOLOGY 



limits for the great majority of organisms being about 16 C. 

 and 40 C. In practice two temperatures are all that are used 

 for ordinary work. The lower, or so-called " room tempera- 

 ture," is about 20 C. (68 F.), and is of most use for those 

 bacteria which grow naturally outside the body i.e., as sapro- 

 phytes. The higher, or body temperature, is about 37 C. 

 (98*6 F.), and is the best temperature for the majority of 

 germs which live within the body i.e., the parasites. It is 

 obvious that gelatin cannot be incubated at this high tem- 

 perature, as it melts at 25 C. or thereabouts; but all other 

 media are available. 



The term " room temperature " must not mislead the practi- 

 tioner, for the temperature of many rooms is not constant at 

 or near 20 C. for periods sufficiently long to permit of its use 

 for incubating bacteria. In the laboratory we use an incu- 

 bator, the temperature of which is regulated by means of an 

 automatic regulator, 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 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 temperature may melt the gelatin, while the 

 latter will only delay the growth of the colonies. It will 

 probably be necessary to find one such place in the hot weather 

 (e.g., the cellar) and another one in the winner (e.g., a cup- 

 board not far from the hot-water pipes). 



It is necessary that cultures which are being incubated 

 should be kept in the dark, as light is inimical to the develop- 

 ment of nearly all bacteria. 



Incubation at the body temperature presents more difficulty. 

 An incubator is almost essential when much work has to be 

 done. Messrs. Hearson, who have such a high reputation for 

 this class of apparatus, have recently devised at my sugges- 

 tion a simple and excellent incubator specially for the general 

 practitioner who does not want a large one, and who will not 

 have it in constant use. It should be kept empty when not 

 required, and when cultures have to be incubated, the water- 

 jacket must be filled with water at body heat and the gas or 

 lamp lit, or, in the case of an electric apparatus, the current 



