238 THE CAUSATION OF DISEASE. 



diseases, but which now, by a gradual process of adaptation on 

 the part of our forefathers, have become powerless to do harm ? 



A curious fact which I have recently learned tends in some 

 measure to confirm these views. According to the Rev. J. 

 Williams, the first intercourse between natives and Europeans "is 

 universally attended with the introduction of fever, dysentery, 

 or some other disease, which carries off numbers of the people. 

 . . . Most of the diseases," he continues, " which have raged 



in ■ ■ during my residence there have been introduced by 



ships, and what renders this fact remarkable is that there 

 might be no appearance of disease among the crew of the ship 

 which conveyed this destructive importation."* Darwin also 

 observes that " the first meeting of distinct and separate 

 peoples generates disease." Now these facts show that each 

 separate community is exposed to some specific form, or forms, 

 of E, which, although perfectly innocuous to itself, may be 

 distinctly pathogenic to others. What is the exact nature of 

 the pathogenic E or E's in each case it is impossible to say, 

 but it is probable that the virus is not that of any well-known 

 " specific " fever. The important fact to remember is that 

 each community is perfectly adapted to its particular virus, or 

 varieties of virus. This adaptation may be the result of natural 

 selection continued through long ages. Nevertheless there is 

 evidence that the mere congregation of individuals may beget 

 a poison to which gradual personal adaptation may occur. 



In the Black Assizes, for instance, the prisoners brought to 

 trial from the putrid gaols communicated a fatal form of fever 

 to the judges sitting in court, the prisoners themselves heing quite 

 free from any trace of fever. Now, seeing that the latter must 

 have swarmed with the morbid germs, it seems probable that 

 they had gradually become adapted to the mal-E of the prisons, 

 just as a mouse can in some measure adapt itself to an atmo- 

 sphere exhausted by respiration ; for if one of these animals be 

 placed in a vessel till the air has been in this way greatly 

 exhausted, and a second one be then introduced, the latter will 

 be the first to succumb, showing that a certain amount of 

 adaptation has occurred in the survivor. The same line of 

 argument might be applied to the prisoners of the Black Assizes. 

 * Quoted by Sir William Aitkin : "Evolution in Pathology." 



