THE GEOGKAPHICAL PAEALLEL 21 



Germany is to be regarded as the original home of syphilis. 

 Whichever view be accepted it is clear that we deal with an 

 infection which is not coeval with the appearance of man. Either 

 we deal with a disease which made its first appearance within 

 historical time, or a disease which appeared in America long 

 after the New World became separated from the Old — and there, 

 it may be, appeared in Haiti and the West Indies after these 

 were separated from the mainland. If the former view be 

 correct we have a further example of the phenomenon imme- 

 diately under review — if the latter, another of the many examples 

 of diseases peculiar to one district, which may or may not eventu- 

 ally spread to other parts of the world. As Major Strong and 

 the Harvard Commission have recently shown, there are human 

 diseases peculiar to South America. There is a " blastomycosis " 

 peculiar to the San Joaquin Valley in California. We know 

 that Measles was unknown to the Pacific Islands prior to the 

 eighteenth century, that cholera, endemic in the delta of the 

 Ganges, similarly only spread along the trade routes to the 

 rest of the world early in last century. 



The Parallel of Geographical Distribution 



This last group of cases — and it might be added to exten- 

 sively — is exactly parallel to what has been ascertained regarding 

 the geographical distribution of animals. To afford an easily" 

 grasped illustration I may note what we may term the epizootic 

 which followed the introduction of the European rabbit into 

 Australia, or the English sparrow into North America. Now 

 rabbit and sparrow are relatively old species : the reason why 

 they had not hitherto been present in areas eminently adapted 

 for their existence, is that they made their appearance in the 

 Old World at some period subsequent to the separation of the 

 New World and Australia from the Old. There are, I know, 

 other considerations to be taken into account : I might, that 

 is, have selected more convincing examples from among the 

 abundant data regarding the geographical distribution of animals, 

 but these will serve as familiar examples. 



The very fact, therefore, that certain highly infectious 

 diseases may be traced to a previous or existing limited and 

 localized incidence, is a proof that their origin is to be dated 



