VARIETIES OF STREPTOCOCCI 203 



the longest chains grow most distinctly in the form of spherical 

 granules, those forming short chains giving rise to a finer deposit. 

 To a variety which forms distinct spherules of minute size the 

 term streptococcus conglomeratus has been given. 



Varieties of Streptococci. — Formerly the streptococcus pyogenes 

 and the streptococcus erysipeloids were regarded as two distinct 

 species, and various points of difference between them were 

 given. Further study, and especially the results obtained by 

 modifying the virulence (p. 175), have shown that these dis- 

 tinctions cannot be maintained, and now practically all authorities 

 are agreed that the two organisms are one and the same, 

 erysipelas being produced when the streptococcus pyogenes of a 

 certain standard of virulence gains entrance to the lymphatics of 

 the skin. Petruschky, moreover, showed conclusively by inocu- 

 lation that a streptococcus cultivated from pus could cause 

 erysipelas in the human subject. 



Streptococci have also been classified according to the length 

 of the chains. Thus there have been distinguished (a) strepto- 

 coccus longus, which occurs in long chains and is pathogenic to 

 rabbits and mice ; (6) streptococcus brevis, which is common in 

 the mouth in normal conditions, and is usually non-pathogenic ; 

 and (c) streptococcus conglomeratus, so called from its forming in 

 bouillon minute granules composed of very long chains. French 

 writers describe a short-chained variety under the title entero- 

 eoccus ; this for convenience will be described separately. It 

 may be stated that pathogenic streptococci obtained from .the 

 human subject usually form fairly long chains on agar, whilst 

 the short streptococci obtained from the mouth and intestine are 

 usually devoid of virulence. But to these statements exceptions 

 occur, as short streptococci may be associated with grave lesions, 

 and long streptococci without virulence may be obtained on 

 normal mucous membranes. Recently anaerobic streptococci 

 have been isolated from war wounds (Fleming). In view of all 

 the facts, pathogenicity and morphology cannot be taken as 

 affording in themselves a basis of classification. Accordingly, 

 other methods have been introduced as a means of differentiation, 

 and of these the most important are fermentation and hemolytic 

 tests. 



Fermentation. — Mervyn Gordon introduced for this purpose nine tests, 

 namely: (1) The clotting of.milk, (2) the reduction of neutral-red, (3-9) 

 the fermentation with acid production of saccharose, lactose, raffinose, 

 inulin, salicin, coniferin, and mannite. Andrewes and Horder by means 

 of these have differentiated six varieties, of which five occur in the human 

 subject. These are : (a) A short ; cbained form called streptococcus mitis, 

 which occurs chiefly in the saliva and faeces as a saprophyte. It ferments 



