GENUS BACTERIUM 287 



Cultivation. The media in which the most characteristic 

 growth appears are blood serum, serum agar, bouillon and 

 milk. 



Agar. The growth on agar is very slow and scanty. This 

 medium has been found unsuitable for the growth of Bad. 

 pyogenes. 



Gelatin. This is not a favorable medium for the isolation 

 and cultivation of Bact. pyogenes, for it is soon crowded out 

 by a growth of other microorganisms. In and upon serum- 

 gelatin, the growth is not much better than upon gelatin. 



Blood serum. According to Berger a characteristic growth 

 appears upon this medium. In twenty-four hours after inocu- 

 lation, very small clear colonies appear. At first there are 

 slight depressions in the surface ; a day or two later a furrow 

 forms along the line of inoculation which gradually becomes 

 deeper as the serum liquefies. In this furrow, or near it, are 

 sometimes found deeper depressions. In these, in old cultures 

 in the vegetative form, are to be seen dull white, fine "kernels" 

 of growth. The surface of the serum is moist and shiny. In 

 the condensation water, a white precipitation forms, but the 

 liquid itself remains clear. Soon the condensation water and 

 the liquefied serum mix together. As the culture grows older, 

 liquefaction increases, so that the culture medium divides and 

 particles of serum float in the clear fluid. Finally, not very 

 much remains of the solidified serum, but in its place is the 

 clear liquid. 



Potato. It does not grow on this medium. 



Bouillon. Growth in bouillon is very slight. 



Liquid serum. After 24 hours from the time of inocula- 

 tion, a slight growth is visible in this medium. It forms a 

 thick gray sediment which is easily stirred up by shaking the 

 flask containing it. The liquid remains clear. The bacilli do 

 not live long in this medium. 



Serum bouillon. A thick, gray, flaky sediment forms. 

 This medium was found to be more favorable than milk. For 

 the best results, the quantity of serum should be less than that 

 of bouillon. 



