4 INTRODUCTION. 



its support, supplies the means by wliich the peculiar chemical 

 composition, characteristic of each individual being, is preserved; 

 at death, on the cessation of this interchange of matter, the organic 

 substance passes into solution or putrefaction. Instead of those 

 complex combinations of elements, which form the proximate con- 

 stituents of organic bodies, simpler combinations arise, which being 

 taken up by the air or the earth, become anew the vital stimulants 

 and the nutriment of that vegetable world, on whose existence the 

 life of animals is dependent. Thus we perceive here an interchange 

 of matter on a large scale, as we do in every organic being on a 

 small one : and perishableness becomes the means whereby new life 

 and fresh youth are effused over the whole of nature 1 . 



Plants and Animals. 



The above may suffice to give a general notion of organised 

 bodies. It scarcely requires notice that the term includes plants 

 and animals. 



At first sight it seems easy to distinguish an animal from a 

 plant : and even the most unskilled person thinks he has a clear 

 notion of the difference. Yet it is just his want of knowledge that 

 causes the difference to appear so prominent : whilst he overlooks 

 the intermediate links, and thinks, for instance, of a dog and a 

 pear-tree. There are two sorts of judgment with conviction. Such 

 a judgment may arise either from want of knowledge, or from pro- 

 found insight, the result of long and accurate investigation. Who- 

 ever seeks after truth must learn to sacrifice the first, even though 

 he may never attain to the second. 



Animals are usually considered as more composite and more 

 perfect than plants. Yet when we compare the simple substance of 

 which Infusory Animals and Polypi are composed with the orderly 

 and beautiful structure of the higher plants, we become satisfied 

 that this proposition is far from having a general value. 



It is said, plants are rooted in the ground, and by this token 

 are sufficiently distinguished from animals. But it is here over- 

 looked, that there are free-swimming water-plants, just as there are 



Ut opus natures perenni flore rideat." LINN>EUS. 



