THE OPTIMISM OF PATHOLOGY 303 



holism out of place, out of time, and out of tune, 

 and Nature makes short work of such unhandy 

 idiosyncrasies. What then of potato disease and 

 salmon disease, of fowl cholera and swine fever, 

 and big-bud on our currant bushes and bee-disease 

 in our hives? The list may be lengthened out, 

 but the answer is probably the same in all cases, 

 that these diseases are microbic or parasitic, not 

 constitutional, and that they occur in artificial, 

 humanly-contrived conditions, not in the economy 

 of wild Nature. There are very few examples of 

 microbic diseases in natural conditions, one of the 

 best known being a bacterial disease in sandhoppers, 

 and this may, for all we know, have something to 

 do with sewage or the like. It is not denied that 

 wild animals are sometimes widely infected with 

 microbes so that an epidemic results. We know of 

 a sort of diphtheria among ring-doves, and it may 

 be that some disease was responsible for the extra- 

 ordinarily rapid disappearance of the Passenger 

 Pigeon. But what is maintained is that such 

 occurrences are rare and evanescent, and that they 

 are usually traceable to rapid human interference 

 to introducing new tenants into a region, to killing 

 off the natural eliminators of the sickly, to per- 

 mitting overcrowding, to an infection of the soil 

 and water, and so forth. As to grouse, it seems 

 that there is no specific disease in this well-nigh 

 sacred bird, but that the removal of natural sifting 

 agencies allows of the accumulation of weaklings 

 and weaknesses. The contingent of parasites which 



