186 ATLAS OF BACTERIOLOGY. 



culture of pathogenic varieties, which thrive with 

 difficulty or not at all upon other nutrient media. 

 Plate cultures are only possible with glycerin agar 

 and mixtures of agar and serum. 

 3. Potatoes. 



(1) To obtain macroscopically characteristic cul- 

 tures of great durability and for differential diag- 

 nosis. 



(2) Occasionally for the development of spores. 



3. A FEW WORDS ON THE MANIPULATION OF ORDINARY 

 CULTURES. 



The platinum needle must be brought to a glow 

 throughout its entire length each time before using 

 and before putting it away. 



(a) Fluid cultures are inoculated with a loopful of 

 pure culture. 



(b) Gelatin and agar stick cultures are made with a 

 straight needle without a loop, only one puncture to 

 each tube but extending nearly to the bottom. 



(c) Agar and gelatin streak cultures and potato cul- 

 tures are made by a gentle superficial stroke upon the 

 surface with the platinum loop. In the case of the 

 potato it is sometimes necessary to rub the culture in. 



(d) Gelatin plate cultures. 



1. To isolate definite germs in the pure culture. 

 We melt three gelatin tubes ; put into the first, after 

 it has been cooled to 30, a loopful of a fluid culture 

 or a trace of a solid culture; shake the tube while 

 turning it upside down, and then convey from this 

 one or two loopfuls of liquefied gelatin into a second 

 tube. After shaking this, two to three loopfuls are 



