BACTERIA CULTIVATION 



III 



circumstances, and is certainly the best for media containing 

 carbohydrates of any kind. To be effective, the media must be 

 exposed to a temperature of iooC. for thirty minutes, that is, 

 thirty minutes after the steam has begun to form. Overheating 

 of sugars causes them to caramelize and turn black. 



FIG. 24. Incubator. 



Bacteria that grow best at a temperature of 37C. (most of the 

 pathogenic ones do) develop more rapidly and luxuriantly in an 

 incubator, or thermostat. Indeed some organisms, like the 

 tubercle bacillus, cannot be cultivated without it. An incubator 

 comprises an air chamber surrounded by a water chamber, and 

 this, in turn, is surrounded by another air chamber. It is essen- 

 tial that the interior of the incubator be kept at an even, unvary- 

 ing temperature. This is accomplished by using a small bunsen 

 flame under the incubator. The heat from the flame warms the 

 outer air chamber or jacket, and it in turn warms the water 



