448 BACTERIOLOGY. 



One now has a meat-infusion-peptone-nutrose-agar 

 with 13 per cent, of litmus solution and 0.01 per thou- 

 sand crystal violet, which becomes very hard on solidi- 

 fying, without becoming too dry. Plates are poured 

 with this material which can be held in readiness for 

 some time, and the remainder of the medium is placed 

 in flasks in portions of 200 c.c. each. 



If the lactose is boiled for a longer time than directed 

 it is reduced with an acid reaction of the culture medium 

 and the content in lactose falls below the required quan- 

 tity, and the alteration in the color of the colon colonies 

 appears too early. For this reason it is also necessary 

 to liquefy the agar as quickly as possible in pouring 

 plates from the agar medium stored in flasks. 



In employing this culture medium it is necessary to 

 have a uniform suspension of a portion of the material to 

 be examined and to make a series of plate inoculations 

 from this suspension. These plate inoculations are best 

 made by means of a sterile glass spatula. 



After fourteen to sixteen hours at 37 C., and still 

 better after twenty to twenty-four hours, the cultures 

 are readily differentiated : 



a. Bacillus coli: All cultures of true colon that have 

 been examined form colonies of 2 to 6 or more millimetres 

 in diameter, of reddish color and translucent. In each intes- 

 tinal evacuation there are usually several varieties of colon 

 colonies which differ according to their size and texture, 

 translucency, and the intensity of the alteration of the 

 color which they bring about. Many colon colonies are 

 bright red, some are cloudy, and others are quite opaque, 

 dark-wine red in color, while still others form large col- 

 onies which are surrounded by a red halo. 



b. Bacillus typhosus: The colonies have a diameter 



