in their Structure aJid Functions, 387 



cess of generation, from pre-existing germs ; and that they 

 terminate their existence by death. Such are the distinctive 

 characters of life; and these characters we find as strongly 

 exhibited in the vegetable as in the animal world. In the 

 next place, when we take a plant for examination, we observe 

 that, Hke an animal, it is composed of solid and fluid parts. 

 The former are fixed and permanent, and constitute the re- 

 ceptacles in which the latter are contained. The fluids, on 

 the other hand, are generally in motion, and are undergoing 

 Some change, either in their quantity, their mechanical admix- 

 ture, or their chemical composition. The solid parts both of 

 vegetables and animals, great as their number and varied as 

 their characters are known to be, are all derived from a few 

 primitive or elementary .forms. In vegetables, these element- 

 ary forms are found to consist of membranous and fibrous 

 matter ; and from these two substances alone the roots, the 

 stem, the branches, the leaves, the bark, the sap-tubes, and 

 the pith are all produced. The elementary solid materials of 

 animals, like those of vegetable bodies, consist of membrane 

 and of fibre ; the former constituting what is termed the cel- 

 lular tissue, the latter forming the muscular and the nervous 

 tissues. From these three tissues, the bones, the muscles, the 

 ligaments, the cartilages, the nerves, the skin, and all the 

 other animal solids, derive their formation. As we proceed 

 farther in our investigations, we discover that membranous 

 matter is a less elementary form than fibrous matter, for all 

 the membranes belonging both to vegetables and animals are 

 composed of fibres, regularly arranged and united together. 

 As we advance still farther, however, we find out that even 

 the fibrous structures are not the real primitive forms of 

 organised bodies, but that they also are produced from other 

 forms, which possess a structure much more simple than that 

 which they present. If we go on another step, we ascertain 

 that the true primitive forms, whence all the elementary tissues 

 to which I have referred are produced, consist of extremely 

 minute spheres or vesicles, and of spicular-shaped bodies. 

 They are seen to be evolved from every organising fluid, 

 vegetable as well as animal, while it is passing fi'om the fluid 

 to the solid state. It is therefore evident, from what has been 

 advanced, that every organised structure, whether it be of 

 vegetable or of animal origin, is composed either of membrane 

 or of fibre. It is likewise evident, that every membrane, both 

 vegetable and animal, is formed of fibres disposed in a regular 

 manner ; that the fibres themselves consist of vesicles and 

 spicula ; and that these two last are to be regarded as the 

 true elementary organised molecules, because we can only 



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