120 BACTERIOLOGY OF THE EYE 



note many differentiating points. In many localities, on the other 

 hand, only one or the other of these infections occurs, and then the 

 probable diagnosis is similarly restricted. For example, in Eostock, 

 Breslau, and Marburg I have almost invariably been able to confirm 

 the provisional diagnosis of pneumococcal conjunctivitis ; but in 

 Freiburg, where Koch-Weeks conjunctivitis is common, such uni- 

 formity does not occur. 1 



The signs and symptoms of a conjunctivitis depend not only on the 

 pathogenic power of the Bacteria, but also on the condition of the 

 nidus, for the latter has a very varying disposition towards different 

 Bacteria. I do not mean by this the variable opportunity for infec- 

 tion, which depends on chance external conditions 2 hygiene, indolent 

 habits, etc. but the actual variation in susceptibility. 



Disposition is a factor of very varying influence in infectious 

 diseases; but, after extreme views have had time to subside, pure 

 bacteriological interpretations always succeed in obtaining recognition 

 of their value. That disposition plays an important part in many 

 eye infections is self-evident. 



This point, however, deserves special consideration, because many 

 surgeons have quite recently raised the objection that the same 

 organisms e.g., diphtheria bacilli and Pneumococci are met with 

 in diseases which are clinically different ; they also occasionally occur 

 on the healthy conjunctiva. 



The sharp differentiation previously made between pathogenic and 

 non-pathogenic saprophytic organisms has gradually been toned down 

 by bacteriologists, as in each natural family many transitional forms, 

 obviously developed from the same origin, became known. Many 

 Bacteria considered as non-pathogenic and purely saprophytic have 

 been shown to cause disease occasionally ; and the pathogenic forms 

 can lose their virulence to such a degree that they become neutral, 

 just as the other morphological and biological properties of the 

 Bacteria can vary. 



Many groups or families have thus been evolved, into which the 

 allied varieties are collected, and the problem to decide is, What 

 relation do their various members bear to each other ? In ophthalmic 

 bacteriology we have problems of this kind to solve. The group of the 

 septate Bacteria i.e., the diphtheria group, the Staphylococcus group, 



1 Of. Usher and Fraser's provisional diagnosis in 86'4 per cent, of Koch- Weeks cases in 

 Aberdeen, where pneumococcal conjunctivitis is very rare. -TRANSLATOR. 



2 0. Rosenthal, under direction of von Michel, has experimentally shown how far 

 spectacles protect against contamination liy dust or moisture (they have practically no 

 action), and how far infected spectacles carry infection (they do so freely). 



