CULTIVATION OF BACTERIA. 201 



planted in the culture-medium, allowed to grow for 

 upward of twelve hours, and then subjected to the com- 

 bined action of a nitrite and chemically pure sulphuric 

 acid. In making the test, Smith adds to each tube i c.cm. 

 of a o.oi per cent, solution of KN0 2 , freshly prepared, 

 and 10 drops of chemically pure H 2 SO<. The presence 

 of indol is characterized by the production of a red 

 color. 



It is not intended that the student shall infer that 

 there are no culture-media other than these, which have 

 been selected because of their usefulness and popularity. 

 Many other compounds and as many simple substances 

 are employed ; for example, eggs, white of egg } urine, 

 bread, sputum, sugar solutions, hydrocele fluid, aqueous 

 humor, etc. 



