NUTRIENT MEDIA. 



47 



makes a good container in which they can be lowered in the 

 Koch's oven. They are left in steam of 100 C. one hour for 

 three successive days, after which the tubes and bouillon are 

 ready for use. 



Solid Media. The knowledge of bacteria and germs or moulds 

 settling and growing upon slices of potato exposed to the air, led 

 to the use of solid media for the artificial culture of the same. 

 It was also thus learned that each germ tends to form a separate 

 colony and remain isolated. 



Potato-Cultures. A ripe potato with a smooth skin is the 

 best. 



Several are brushed and scrubbed with water to get rid of the 

 dirt and the " eyes" are cut out. 



Next placed in 1 to 500 solution of bichloride of mercury for 

 hour. Then in the steam-chest for f hour. 



In the meantime, a receptable is prepared for them. This is 

 called the moist chamber. 



The moist chamber consists of two large shallow dishes, one, 

 the larger, as a cover to the other. 



These dishes are washed in warm distilled water. 



A layer of filter paper moistened with a 15 to 30 drops of 1 to 

 1000 bichloride is placed in the bottom of the glass dish. 



FIG. 20. 



Moist chamber for potatoes. 



The operator now prepares his own hands, rolling up his coat 

 sleeves and carefully washing his hands, then taking a potato 

 from the steam-oven and holding it between his thumb and 

 index finger in the short axis, he divides the potato in its 

 long axis with a knife that has been passed through the flame. 

 The two halves are kept in contact until they are lowered into 



