preserving, i.e., careless elimination of the natural enemies, 

 removes the natural sieves, then birds of weakly constitution 

 tend to become more numerous with each year, till a bathos 

 of weakness is reached. The contingent of parasites which 

 seems to be kept within limits in the vigorous bird may then 

 increase sevenfold, spreading, for instance, to new organs, and 

 this may give the death-blow. It seems that there is no spe- 

 cific disease in this well-nigh sacred bird, and it is highly 

 probable that there would be no ( grouse-disease ' if there 

 were no game-keepers. 



5. Parasitism. 



One of the shadows on the pleasant picture of animate 

 nature is the frequency of parasitism. To some minds it 

 appears as a blot spoiling the whole script. But without 

 denying that there is some warrant for practical, aesthetic, 

 and ethical recoil, we think that much of this is due to lack 

 of perspective. Let us briefly consider the facts of the case, 

 (a) Thousands of living creatures live in or on others, 

 Abound up with them in brutally direct nutritive dependence, 

 and incapable of living in any other way. Uninvited and 

 non-paying boarders they are, who make their hosts no re- 

 turn for the hospitality enjoyed. Most animals that have 

 bodies at all have parasites in or on them, and the same 

 is true of most of the higher plants which are the hosts of 

 moulds and rusts, gall-producing creatures, and burrowing 

 larvae. One of the European oaks harbours no fewer than 

 ninety and nine different kinds of gall-flies, and the hun- 

 dredth is probably being discovered. The lac insect of India 

 is attacked by thirty-one species of plant and animal para- 

 sites. The dog is a terrain for over forty parasites; man 

 and pig have far more. In fact when we inquire into the 



