338 



BACTERIA PATHOGENIC TO MAN 



parts of a single colony. They multiply by binary division in one 

 direction only, forming chains of eight, ten, twenty, and more ele- 

 ments, being, however, often associated distinctly in pairs. On solid 

 media the cocci occur frequently as diplococci, but usually they 

 grow in longer or shorter chains. Certain cocci frequently exceed 

 their fellows greatly in size, especially in old cultures, when this may 



FIG. 104 



FIG. 105 



Streptococci in peritoneal fluid, partly enclosed 

 in leukocytes. X 1000 diameters. 



Streptococci in throat exudate smeared o 

 cover-glass. X 1000 diameters. 



be considered to be the result of involution forms. Some varieties 

 have distinct capsules when growing in the blood and in blood-serum, 

 media (Hiss). 



FIG. 106 



FIG. 107 







Streptococci from solidified serum culture appear- 

 ing mostly in diplococci. X 1000 diameters. 



Streptococcus growing in long chains ii> 

 bouillon culture. X 1000 diameters. 



Staining. They stain readily by aniline colors and the pyogenic 

 varieties positively by Gram's method. Some varieties, mostly sapro- 

 phytic, growing in short chains are negative to Gram's stain. 



Biology. Streptococci grow readily in various liquid and solid cul- 

 ture media. The most favorable temperature for their development 

 is from 30 to 37 C., but they multiply rather freely at ordinary room- 



