SYSTEMATIC AND DESCRIPTIVE. 285 



Potato -cultivations. A very characteristic growth 

 results from the inoculation of sterilised potatoes. 

 The damp-chamber containing the potatoes is 

 placed in the incubator, and in about thirty-six 

 to forty-eight hours a creamy, very faintly yellow- 

 ish layer forms over the inoculated surface, with 

 usually a peculiar translucent edge (Plate XV., 

 Fig. i). On removing the cover of the damp- 

 chamber a strong, penetrating odour of sour milk 

 is encountered. 



FIG. 108. COLONIES IN A PLATE-CULTIVATION, X 70. 



Plate-cultivations. From the spleen or blood of 

 the heart, cultivations must be established in 

 nutrient gelatine on plates. The colonies develop 

 in about two days, according to the temperature of 

 the room. They appear to the naked eye as little 

 white spots or specks, which, on examination with 

 a low power of the microscope and small diaphragm, 

 exhibit two distinct forms. One form, on careful 

 focussing, has the appearance of a little compact 

 ball of twisted thread ; in the other, liquefaction 

 of the gelatine has commenced, and the thread 



