STREPTOCOCCUS PYOGENES 179 



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 faeces 

 as a saprophyte. (6) The streptococcus pyogenes, which is the 

 most important pathogenic variety, and has the characters 

 described above, (c) The streptococcus salivarius, which corre- 

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

 regards fermentative action, seems to bear the same relation to 

 the next variety as the streptococcus mitis does to the strepto- 

 coccus pyogenes. It has more active fermentative properties 

 and clots milk, (d) The streptococcus anginosus, which corre- 

 sponds with the so-called streptococcus scarlatinae and the strepto- 

 coccus conglomeratus. It usually clots milk and does not grow 

 on gelatin at 20 C. (e) The streptococcus fcecalis, a short- 

 chained form, which abounds in the intestine and which has 

 great fermentative activity. It forms sulphuretted hydrogen, 

 and is devoid of haemolytic action. (/) The sixth variety is the 

 streptococcus equinus, which is common in the air and dust of 

 towns, and appears to be derived from horse dung. 1 



Schottmuller has employed the appearance of the colonies of 



^streptococci on blood agar as a means of separating varieties, 

 the medium used consisting of two parts human blood and five 

 parts melted agar. He distinguishes the streptococcus lon<jus or 

 erysipelcitis- which forms __grey colonies and^ _ ^ 

 action i a, streptococcus mitior or mW^^o * 

 organism, which produces small green colonies and very little 



-haemolysis-. and a streptococcus mucosus encapsulates, which, as 



its name indicates, snows well-marked capsules, and produces 



colonies which have a slimy consistence/ It should be noted 



^thaton blood agar the ~pneumococcus forms green colonies andj 



produces no hcemolysyf. 



1 For further details reference niust be made to the original papers, Lancet, 

 September 1906, ii, 708, etc. 



I 



niust be mad 



/VU>VA 



