NUTRIENT MEDIA 51 



their contents in the steam-chest. They are left in steam of 

 100 C. fifteen minutes for three successive days, after which 

 the tubes and bouillon are ready for use. 



Solid Media. The knowledge of bacteria and germs or 

 molds 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 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 i : 500 solution of bichlorid of mercury for 

 one-half hour. Then in the steam-chest for three-quarters 

 of an hour. 



In the mean time a receptacle is prepared for them. This 

 is called the moist chamber. 



Fig. 20. Moist chamber for potatoes. 



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

 the larger, as a cover to the other (Fig. 20) . 



These dishes are washed in warm distilled water. 



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

 i : 1000 bichlorid solution is placed in the bottom of the glass 

 dish. 



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 



