INCUBATION OF CULTURES 



21 



vent evaporation, which greatly hastens the process of cool- 

 jug). The water and culture-tube cool very gradually, and 

 most pathogenic organisms will give an excellent growth 

 before this happens. The Dewar's flask should have a capacity 

 of 600 c.c. and an internal diameter at the neck of i inch or so. 

 It can be supported on a jam-pot with a layer of cotton-wool 

 round the neck. I find it cools at the rate of about half or 

 two-thirds of a degree per hour. 



The author once succeeded in making a diagnosis in a case 

 of supposed diphtheria by the following method : The tube of 

 medium was inoculated from the throat, and placed in a jam-pot 



FIG. 8. DEWAR'S FLASK ADAPTED FOR USE AS INCUBATOR. 



a, Culture tube ; b, vacuum ; c, water ; d, layer of oil ; e, cotton-wool round 

 mouth of jar for support. 



which was partly filled with water at 37 C.; a thermometer 

 was also inserted, and the whole placed near the fire. It was 

 watched from time to time, and moved near the fire if the tem- 

 perature showed signs of falling-, and vice versa, until the 

 proper position was found. Next morning there was an 

 excellent growth, and the diagnosis was made with certainty. 

 Lastly, the author has heard of a practitioner who was in 

 the habit of incubating cultures at the body temperature by 

 carrying* them in an inner pocket during the day, and taking 

 them to bed with him at night ! * 



* Since the above was written an incubator to be used in this way has 

 been invented. 



