GELATIN AND POTATO MEDIA. 



179 



a maximum flow the temperature in the inner compartment will be 

 the minimum attainable. In this laboratory the temperature of the 

 water during summer, as it comes from the ground, is 14^15°. This 

 represents, then the lowest constant temperature attainable. By 

 diminishing the flow of the water, heat is absorbed, and a higher 

 temperature can be obtained. The inner compartment can thus be 

 maintained at 18°, 20° or 22°. In the apparatus, as actually used, the 

 flow is such that a temperature of 18-20° is maintained throughout 

 the summer months. It is well to keep inside of the apparatus a. 

 Kappeler maximum and minimum thermometer. 



Fig. 33. The author's constant, low temperature apparatus. 



Laboratory work.— The student will make plate cultures of the 

 Bacillus prodigiosus and of Bacillus Indicus. The potato cultures 

 made heretofore will supply the material for inoculation. 



Modified Gelatin Plate Cultures. 



The original plate method of Koch, as described on 

 p. 172, has been subjected to several modifications, some of 

 which may be considered as decided improvements. The 

 iron box, plates, benches, moist-chambers and levelling- ap- 



