INCUBATION OF CULTURES 



21 



Another method I have recently adopted is to use a "Thermos " 

 flask, or, what comes to the same thing, a Dewar's liquid air 

 flask. This is nearly filled with water at a temperature of about 

 40° C. and the culture-tube inserted. If a Thermos is used the 

 cap is then applied, if a Dewar's flask a few drops of oil are 

 placed on the surface of the water (to prevent evaporation, which 

 greatly hastens the process of cooling). 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. 



Fig. 12. — 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. 



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 

 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 temperature 

 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 



