THE GENUS STREPTOCOCCUS l6l 



of these forms to a mountain range, with peaks and con- 

 necting valleys between, has been quoted in an earlier 

 chapter. The essential point in their work was the 

 establishment of the fact that type centers occur among 

 the streptococci, about which most of the cultures found 

 in nature group themselves more or less closely. Further- 

 more these types are in most cases associated with defi- 

 nite habitats, — a strong point in favor of their systematic 

 significance. The division between types is not, of course, 

 a sharp one. The centers to which Andrewes and Horder 

 have given names shade off into each other by imper- 

 ceptible gradations. Yet "this indefinite state of affairs 

 actually represents the condition found in nature." The 

 scheme outlined "fairly represents the actual medley of 

 types seen in nature, and the way in which, by the processes 

 of evolution, nature herself is sorting out the medley." 

 "Some such conception of the streptococci as we have set 

 forth is preferable to the idea that they are all one kind 

 or that they present a hopeless chaos. " 



With this preamble, Andrewes and Horder proceed to 

 define seven species of streptococci (including the pneu- 

 mococcus) as follows: 



i. Streptococcus equinus (Andrewes and Horder). 

 This type of streptococcus appears to be characteristic of 

 the intestine of the herbivora. It is abundant in horse 

 dung and is the commonest form in the air of London. It 

 forms chains of medium length, grows feebly, if at all, at 

 20 degrees, and ferments saccharose and the glucosides 



