GENUS STREPTOCOCCUS 195 



of a specific infection. Migula describes about 80 species of 

 which very few are pathogenic for animals. 



Morphology and biologic properties of streptococci. The 

 individual streptococcus is a spherical microorganism measur- 

 ing from 0.5 micron to 1 micron in diameter. Since the line 

 of cleavage of cocci, when in chains, is perpendicular to the 

 long axis of the chain, adjacent cocci often show slight flatten- 

 ing of the contiguous surfaces, forming, as it were, a series of 

 diplococci arranged end to end. 



Streptococci are easily stained by the usual aniline dyes. 

 Stained by the method of Gram, the pyogenic streptococci are 

 not decolorized and invariably retain the gentian-violet. Cer- 

 tain species found in stools and described as Gram-negative 

 are rare and are non-pathogenic. Others of the "Streptococ- 

 cus brevis" variety, and purely saprophytic, may stain ir- 

 regularly by the Gram method. 



Cultivation. The pyogenic streptococci are readily cul- 

 tivated on all the richer artificial media. While meat extract- 

 peptone media may suffice for certain strains, it is usually 

 better to employ those which have the beef or veal infusion for 

 a base. For the cultivation of more delicate strains of strep- 

 tococci, especially when taken directly from the animal body, 

 ..it is well to add to the media animal albumin in the form of 

 whole blood, blood serum, or ascitic or pleural transudates. 

 Glucose, added in the proportion of one to two per cent, like- 

 wise renders media more favorable for streptococcus cultiva- 

 tion. Prolonged cultivation of all species upon artificial media 

 renders them less fastidious as to cultural requirements. The 

 most favorable reaction of media for streptococcus cultivation 

 is moderate alkalinity (two-tenths to five-tenths per cent alka- 

 linity to phenolphthalein). Growth may be obtained with 

 many strains, however, in neutral media or even in those 

 slightly acid. Growth ceases at a temperature of 45 C. Many 

 streptococci will develop slowly at room temperature. While 

 the free access of oxygen furnishes the most suitable environ- 

 ment for most races of streptococci, complete anaerobiosis 

 does not prevent the development of most species in favorable 



