436 BACTERIOLOGY. 



nies sometimes present much the same appearance. 

 However, it was found that the typhoid colonies usu- 

 ally grew near the surface, while the colon colonies, 

 which are small and white, are almost invariably very 

 deep. This is especially true after forty-eight hours; 

 therefore, if one is not sure of a colony from the 

 appearance, an attempt to "fish" it will usually 

 identify it. 



To one familiar with the medium, the characteristic 

 appearance of a plate when typhoid is present is almost 

 unmistakable, and it would seem that one would be 

 almost sure to find the typhoid in some one of a 

 series of plates, even if there were but few in the 

 specimen. 



Eisner says that the typhoids do not develop for 

 forty-eight hours. Although the differentiation is 

 more accurate after that time, still for practical 

 methods of work twenty-four hours was found to be 

 quite sufficient. When the plates are first taken from 

 the incubator the diagnosis is not quite as certain, for 

 the colon colonies will not have developed the charac- 

 teristic color; but if the plates be allowed to stand in 

 the light for a couple of hours the diagnosis will be 

 found quite easy. After forty-eight hours all the large 

 colonies will be colon and most of the small ones 

 typhoid, if there be any typhoid present. Even after 

 several days' standing in the ice-chest the typhoid colo- 

 nies do not develop color. 



Except for the difficulty in obtaining an exact tem- 

 perature for growth and a cool room for examination, 

 this method was found very satisfactory. 



THE CAPALDI PLATE MEDIUM. In his original 

 paper, Capaldi gives the following recipe: 



