186 APPLIED BACTERIOLOGY 



erysipelas. By some observers it is believed to be identical 

 with the Streptococcus pyogenes, but it is more probable 

 that there is a group of streptococci which are exceedingly 

 alike in their microscopical and cultural characters. 



The streptococcus, whether in pure culture or in section, 

 can be stained by the ordinary aniline dyes. 



Growth on Media. — The organism grows in peptone-broth, 

 on gelatine, agar or blood serum ; on potato the growth, if 

 any, is imperceptible. The organism grows equally well in 

 the presence or absence of oxygen. When grown in beef- 

 broth at 37° C, the medium becomes turbid in twenty-four 

 hours, and after some three or four days multiplication 

 ceases. Living organisms have, however, been found in the 

 sediment that collects at the bottom of the liquid after so long 

 a period as ninety days, and by recultivating a considerable 

 quantity of this sediment on to fresh media, new growths 

 have been obtained. The cessation of growth in broth after 

 three or four days is due more to the exhaustion of the 

 medium than to the formation of a metabolic product 

 injurious to the growth of the organism. This point is 

 proved by Louis Corbett and W. S. Melsom in a valuable 

 paper in the Journal of Pathology and Bacteriology, vol. iii., 

 November, 1894. Little or no growth takes place in meat- 

 broth that has not been peptonised. In broth cultures 

 the organisms grow out lengthwise into chains of 30 or 

 40 elements, of which the individual cocci may vary very 

 much in size, both large and small cocci being found in one 

 chain. It also sometimes happens that a new chain starts 

 away from one of the cocci in a chain, thus producing 

 branching. The variation in the size of the cocci is also 

 noticed in cultures on other media. 



The growth on gelatine is slow ; the colonies are generally 

 small and discrete, while on agar at 37" C. the colonies are 

 often larger, and sometimes spread into a connected mass, 



