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totality of organisable matter locked up in effete forms, and 

 life thus rendered henceforth impracticable. To prevent 

 such a result the dead organism is eaten up by animals or 

 absorbed by plants. The animals and plants thus employed 

 may be termed ' Nature^ s scavengers ' ; and, according as they 

 do their work well or ill, they must rank as sanitary or 

 anti-sanitary agents. Such beings may be found in almost all 

 the divisions of the animal and vegetable kingdoms, from 

 mammalia and birds down to microscopic fungi. Space will 

 not allow me to enumerate them or to describe their varied 

 and often curious ways of going to work. Suffice it to say 

 that they form three classes : some, which bury polluted and 

 offensive matters in the earth ; some, which devour filth, but 

 confine themselves to this diet alone ; and some, which when 

 besmeared with putrid and infectious matter, settle upon our 

 persons and our food, and thus communicate disease and 

 death. As examples of the first and best class we may 

 mention the sexton-beetle, which buries the carcases of small 

 animals ; and the dung-beetles, which carry down into the 

 earth the excrement of various animals. As instances of 

 the second class we may take the vulture, which devours 

 putrid offal, but gives off from its body a most offensive 

 smell. Lastly, in the third class we have the carrion and 

 dung flies, which may be described as the colporteurs of 

 pestilence. Towards these three different classes reason de- 

 mands that we should adopt a totally different line of policy. 



"But the subject, in addition to its practical importance, has 

 also a profound speculative interest. The efficiency and 

 completeness, or the deficiency and the shortcomings of 

 Nature's agencies for dealing with refuse, throw valuable 

 cross-lights upon the origin of species, and indeed upon the 

 whole issue between the old and the new schools of Biology. 

 The scavengers of the first class we should cherish, defend, 

 and seek to multiply. Those of the second, except they are 

 otherwise dangerous, like the wolf and the hyaena, we may 

 tolerate and, under certain circumstances, we may even protect. 

 Thus, when sanitary arrangements are defective, it is good 

 policy to preserve vultures by legal enactments. But against 

 the third class, the diffusers of disease, we should wage a 

 systematic and untiring war. 



