RELATIONS OF MAN WITH ANIMALS. 101 



RELATIONS OF MAN WITH EXTERNAL NATURE. 



IN the preceding pages, man's relations with both inorganic, and 

 organic or organized, bodies, whether vegetable or animal, have been 

 fully illustrated. With the inorganic kingdom of nature, man is re- 

 lated, as we have seen, both in regard to the matter which composes, 

 and to the forces which operate within, his frame. As regards the 

 vegetable and animal kingdoms, he is related not only materially, as 

 implied by his dependence upon them for food, clothing, and protection, 

 but with animals, at least, he is both socially and morally connected, 

 as indicated by the employment of those creatures for his use, and by 

 the ties established between himself and them in their domesticated 

 condition. 



To the physiologist, however, there are other and nearer relations 

 of special interest, viz., zoological relations, as between man and ani- 

 mals only ; biological relations, as between man and organized bodies 

 generally, whether animal or vegetable ; and, lastly, physical and 

 chemical relations, as between him and the inorganic world. These 

 last-named relations are included in those which exist between organ- 

 ized and unorganized bodies generally. Each of these three kinds of 

 relation requires to be separately examined. 



RELATIONS OF MAN WITH ANIMALS. 



The zoological relations of man with the animals disclose points of 

 resemblance and of difference between them, exhibited in both struc- 

 tural and functional peculiarities. Modern zoology is founded on 

 what might be termed zoological anatomy, of which human and com- 

 parative anatomy are merely branches, inseparably connected, mutu- 

 ally explaining and assisting each other, and leading the mind to 

 wider views of structure, to the laws of analogy and homology estab- 

 lished by so-called philosophical or transcendental anatomy, and also 

 to strictly scientific, because truly natural, systems of classification. 

 So likewise, there is a zoological physiology, according to which, the 

 modern physiologist, following the example of the anatomist in regard 

 to structure, endeavors to trace a given function through its various 

 degrees of complexity, down to its simplest, and therefore most essen- 

 tial expression. Thus it is, he follows the various sensory endow- 

 ments of man and the higher animals, as exhibited in the phenomena 

 of the special senses, downwards through the animal scale, observes 

 them becoming fewer and simpler, and at last finds, in some lowly 

 organized animal, common sensation alone present, and thus arrives 

 at the simplest expression of sensibility, viz., mere nervous excitability; 

 in other words, he traces the specialized functions of an organ gradu- 

 ally downwards, till it is reduced merely to the vital property of a 

 tissue. So again, tracing downwards the function of absorption, he 

 speedily meets with animals destitute of special lymphatic or lacteal 

 vessels, and in which, therefore, vascular absorption and circulation 



