34 BACTEKIOLOGY OF THE EYE 



very much limited by the fact that varieties intermediate between 

 the various types occur, in which sometimes one characteristic, some- 

 times another, is prominent. 



It is simply impossible to describe as a new variety every strain 

 which does not absolutely coincide with the strains already described, 

 especially as many of their features alter on prolonged cultivation. 



The pathogenic or pyogenic forms are first opposed to the non- 

 pyogenic ones. 



Eegarding the pyogenic characteristics of the Micrococci of the 

 normal conjunctiva, it is undeniable that the term ' pyogenes ' is far 

 too freely used in the literature. Many authors, without making 

 control inoculations, always use this term when dealing with organisms 

 developing the well-known white or yellow colour in agar cultures. 

 In other cases the cornea is infected by making a pocket with the 

 lance and introducing a loopful of the culture ; a purulent reaction 

 is then recorded when an opacity with inflammatory reaction develops, 

 though it heals without perforation. 



The term ' pyogenes,' however, should only be used in those cases 

 where, after such a liberal infection, at least a rather severe inflam- 

 mation results, with transient iritis and slight exudation into the 

 anterior chamber. The inoculation experiment commonly made 

 only shows that large numbers of the organism do cause a certain 

 reaction, and by no means proves that such an organism is really to 

 be considered as the cause of a suppuration or a wound infection, and 

 thus deserve the name 'pyogenes.' If material be removed, either 

 from such a pocket or the ulcer which results, a control research 

 often shows that the cocci introduced very soon die out, and that the 

 inflammatory reaction was not due to any pathogenic development of 

 the organisms, but merely to the introduction of the bodies of the 

 cocci. 



The white Staphylococci of the normal conjunctiva are closely related to the 

 Micrococcus candicans. Old colonies not infrequently show a small projection in 

 the middle, and are marked with concentric lines. They do not appear to be so 

 moist as the Staphylococcus pyogenes, but this varies with the medium. Where 

 colonies have fused, their former margins often are still visible. They do not liquefy 

 gelatine in a stab culture, but rapidly grow over the surface. Their behaviour on 

 this medium, however, is not constant, for liquefaction may commence weeks later. 

 Plate colonies appear darker in the centre and clearer at the periphery, being more 

 or less granular. Under the microscope many strains show very slight tendency to 

 occur in clusters, but, on the contrary, appear as Diplococci, the members of each 

 pair having a narrow interval between them. 



We have rarely found white cocci of the non-liquefying-gelatine variety which can 

 cause a severe inflammatory reaction; and such certainly were never virulently 

 pathogenic. With this limitation the pathogenic properties of the white Staphylo- 



