DISHARMONIES AND OTHER SHADOWS 577 



from parasites and senescence, there is almost no disease 

 in wild Nature. Should a pathological variation arise, and 

 that seems a rarity, it is eliminated before it takes grip. Dis- 

 ease in the system of Nature is a contradiction in terms. Con- 

 stitutional disease is the occurrence of a metabolism out of 

 place, out of time, and out of tune, and Nature makes short 

 work of such idiosyncrasies. 



What, then, of potato disease and salmon disease, of fowl 

 cholera and swine fever, of big-bud on our currant-bushes 

 and bee-disease in our hives? The list may be lengthened 

 out, but the answer is the same for all, that these diseases 

 occur in artificial, humanly contrived conditions, not in the 

 system of wild Nature with which we are here concerned. 

 It is doubtful whether there are more than two or three 

 examples of microbic disease in natural conditions, one of 

 the best known being a bacterial disease in sandhoppers, and 

 this may have something to do with sewage, as salmon-disease 

 with polluted rivers. 



It is not asserted, however, that wild animals may not be 

 infected with microbes so that an epidemic results. What 

 is maintained is that such occurrences are exceedingly rare 

 and transient, 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 permitting over-crowding, to an infection of the soil and 

 water, and so forth. 



What of a familiar case such as grouse-disease? The 

 facts appear to be that grouse harbour a good many parasites 

 which normally do them no appreciable harm. When birds 

 of inherently weakly constitution appear they are normally 

 eliminated by golden eagles, stoats, and other natural ene- 

 mies ; and the standard of the stock is not lowered. If over- 



