The philosophy of natural history / by William Smellie ; with an introduction and various additions and alterations intended to adapt it to the present state of knowledge by John Ware.
- William Smellie
- Date:
- 1827
Licence: Public Domain Mark
Credit: The philosophy of natural history / by William Smellie ; with an introduction and various additions and alterations intended to adapt it to the present state of knowledge by John Ware. Source: Wellcome Collection.
Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)
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![measure the appearance of plants, which are yet without doubt of animal origin. But of these it is to.be remarked, that they are not animals themselves, but the residence of animals; they are substances produced by the labour of myriads of little polypes, who pile them up in order to serve for their covering and habitation; and, although when thus produced they have the externa] shape of vegetables, the creatures themselves, which have produced them, do not bear the smallest resemblance to plants. 7. The chemical composition of vegetables also differs from that of animals. The elements essential to vegetables ore three in number, oxygen, carbon, and hydrogen ; and from these three principally are formed all the different substances which we meet among plants. But, besides these, animals require the presence of azote or nitrogen also, which is necessary to their com- position ; and from this, combined with the others in different proportions, are formed all the parts absolutely essential to animal existence. There are, it is true, many other elements which are found in some parts of plants or animals, but these are all which are absolutely essential to the composition of vegetable or animal substance. Thus in the bark of some plants, beside the three elements necessary to its formation, there will be found a portion of silex or flint; and in the bones of animals, in addition to the four essential elements, lime is deposited in large quantities. So that, although there must always be present at least these neces- sary and specified elements in the composition of vegetables and animals, there is no limit, no principle which precludes the ad- mission of others. In consequence of this difference in chemical composition, and perhaps of the mode in which the elements are combined, other differences of a particular character may be detected between substances of a vegetable and those of an animal origin ; differen- ces which serve in cases of doubt to assist us in deciding to which class any particular substance belongs. Thus, in burning, sub- stances of animal origin always exhale a very peculiar odour, that of burnt wool, feathers, sponge, &,c. an odour easily recog- nised and not readily forgotten. This will always serve to deter- mine whether any particular substance which we examine is de- rived from the vegetable or animal kingdom. Physiologists have frequently busied themselves in endeavour- ing to discover what it is, which distinguishes precisely the two living kingdoms from each other. They have endeavoured in vain, because they have expected to find this distinction in one](https://iiif.wellcomecollection.org/image/b21154661_0023.jp2/full/800%2C/0/default.jpg)
