548 



A MANUAL OF BACTERIOLOGY 



It may form a dry pellicle on the surface of broth, but 

 more usually gives rise to cohering colonies at the bottom 

 of the tube ; in either case the medium remains clear. 



It grows slowly on gelatin, producing a yellowish- 

 white growth and slow liquefaction, beginning about the 

 seventh day. The resulting fluid may or may not be 

 dark- coloured. On blood serum it pro- 

 duces poor growths, and no liquefaction 

 or pigmentation of the medium. 



On agar and glycerin agar it forms 

 hard spherical white colonies, which give 

 rise to an undulating crater if orm growth, 

 having a yellowish or greyish tint, which 

 in time becomes a lichenoid ashen grey or 

 yellowish mass with a powdery efflores- 

 cence. Microscopically the growth consists 

 of masses of filaments (Fig. 50). the ends 

 of which may be somewhat clubbed and 

 segmented, but which never show rosette 

 arrangement of clubs such as occurs in 

 the tissues. On maltose agar it forms 

 discrete fawn - coloured colonies, later 

 becoming yellow, dark brown or even 

 black, while the medium may be slightly 

 darkened. 



On potato it forms confluent, hard, 

 raised, variously coloured masses, at first 

 white but becoming greenish - yellow, 

 brown, greyish-black or even black, with more or less 

 erosion and pigmentation of the medium to which the 

 growth is very adherent (Fig. 51). No diastatic action 

 has been observed. Litmus milk is first reddened, but 

 later it becomes a clear brown alkaline liquid. 



Nocardia bovis infects cattle, swine, horses and occa- 

 sionally man, while experimentally rabbits and guinea- 



FIG. 51. Actino- 

 myces. Potato 

 culture, three 

 months old. 



