212 INFLAMMATION AND SUPPURATION 



that those which form 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 erysipelatis 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. 217), 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 ; (b) 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. 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 ; it 

 has also been found that the length of the chains is not a 

 constant feature. 



As in the case of other organisms, attempts have also been made to 

 differentiate streptococci by means of their fermentative properties. 

 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-chained form called streptococcus mitis, which 

 occurs chiefly in the saliva and f'seces as a saprophyte. It ferments 

 saccharose and lactose, and sometimes the glucosides ; it produces an acid 

 reaction in milk but no clotting, and often reduces neutral-red. (&) The 

 streptococcus pyogenes, which is the most important pathogenic variety, and 

 has the characters described above, (c) The streptococcus salivarius, which 

 corresponds to the streptococcus brevis of the mouth, and which, as 

 regards fermentative action, seems to bear the same relation to the next 



