SPECIAL FORMS OF CONJUNCTIVAL INFECTION 269 



very insufficient. Much of what has been stated with the certainty of 

 law on this subject has been definitely proved untrue, as, for instance, 

 the alleged immunity of the Celts ; and with regard to the other 

 trachoma-free races, it is doubtful whether they really have had any 

 considerable opportunity for infection. This is the case with regard 

 to the alleged immunity of the coloured people in North America (who 

 generally live by themselves), for it has been shown (van Milligan) 

 that people of the same negro races in Europe and Asia are often 

 severely affected. Climatic considerations, especially height above the 

 sea-level, are greatly exaggerated. Low-lying land near rivers and 

 marshy places do appear to be particularly affected, especially in 

 certain countries. In his historical account of trachoma Hirschberg 

 lays particular emphasis on this point, and asks whether the trachoma 

 virus may not be closely related to that of malaria. 



It has often been suggested that some attenuation in the virulence 

 of trachoma occurs through adaptation in affected races, but it is 

 doubtful if such be the case. Certainly at the commencement of the 

 nineteenth century, after the Napoleonic campaigns, severe acute 

 catarrh was more frequently observed ; but this can have been quite 

 well due to the more frequent and epidemic occurrence of the mixed 

 infections referred to above, as, indeed, is the case at the present time 

 in Egypt. The opportunities for infection, and the hygienic conditions 

 which would favour the transference of the infection and intensify 

 the severity of the disease when established, are all important 

 factors. 



A condition of affairs opposed to this idea is seen in many parts of 

 Germany (Rhine Valley and Westphalia), where trachoma is diminish- 

 ing. It is very doubtful whether this is not essentially due to a better 

 hygiene and the spread and improvement of medical attention, rather 

 than to the trachoma becoming worn out and extinct. The suppo- 

 sition brought forward by Peters that the tendency to infection 

 by the ubiquitous trachoma virus is decreasing is also purely hypo- 

 thetical. Thus ubiquity .attributed to the trachoma virus is in the 

 highest degree unlikely, as experience shows that trachoma has 

 always been introduced, and that it forms groups of cases where none 

 were previously present. The indigenous population are naturally 

 only infected when they come into sufficiently close contact with the 

 diseased aliens ; and where this contact does not occur, or does so 

 only to a very limited extent, only very few cases occur among the 

 indigenous population. 



Junius and Schmeichler have rightly shown that this excessive 



