ANIMAL. 



131 



its existence, namely, among the higher tribes 

 of living things, the absorption or ingestion of 

 food or alimentary matter ; the preparation of 

 this food by the processes of digestion and 

 respiration ; the distribution of the nutritive 

 matter fitted for its ends, to every part of the 

 system by means of a circulation ; the conver- 

 sion of the nutritive matter into the solids 

 and fluids or proper substance of the indi- 

 vidual, and finally the depuration and rejection 

 of the worn-out parts and particles by means 

 of certain secreting organs. These various pro- 

 cesses in themselves will be particularly con- 

 sidered in the article NUTRITION, to which the 

 reader is referred. Meantime let us contrast 

 these different functions as they manifest them- 

 selves in each of the two grand divisions of 

 the organized world. 



Assumption of aliment. The earth and 

 the atmosphere, and the carbonic acid 

 and water they contain, are the sources 

 whence vegetables derive their food. Mere 

 they find aliment ready prepared for their use, 

 or rather, as passive agents, they depend on 

 the earth and the atmosphere for a supply 

 of the elements required for their continuance. 

 Those physiologists are now admitted to have 

 been mistaken who supposed that the food of ve- 

 getables was furnished by the inorganic earth, 

 air, and water, with which their roots and 

 leaves are in relation ; more accurate experi- 

 ments have shown that plants are as dependent 

 as animals on supplies of substances that have 

 once had life for their support. When plants 

 are made to grow in pure earth and in distilled 

 water, they appear to do so by a kind of de- 

 composition of themselves, one part perishing 

 and affording food to that which continues to 

 live. To base a distinction between animals 

 and vegetables, consequently, on the presump- 

 tion that the one lived on organic, the other on 

 inorganic substances, was incorrect : animals 

 and vegetables are alike in this respect ; both 

 feed upon organized matter, and this not al- 

 ways or necessarily in a state of decomposition, 

 as we observe among parasitic tribes, which 

 subsist on the living juices of the individuals 

 they cling to. The food of animals, however, 

 may be stated generally to be both more various 

 and also more complex in its chemical com- 

 position than that of vegetables, and whilst 

 vegetables take all their food in a liquid shape, 

 animals much more commonly live on a mix- 

 ture of solids and fluids. 



The assumption of food by vegetables and 

 animals takes place under very different cir- 

 cumstances. In vegetables it is necessary and 

 independent of the individual; it is also in- 

 cessant ; and, farther, it takes place from the 

 external surface, inasmuch as it is with this 

 that the materials which supply the nutriment 

 are in contact. 



Animals, however, have not generally their 

 food prepared for their use brought into con- 

 tact with their bodies, neither are they passive 

 in its assumption ; they have mostly to search 

 for it abroad, and are provided with special 

 organs for this purpose. The act by which 

 they take it is not necessary, neither is it in- 



cessant. They have also to select their food, 

 and are, therefore, furnished with faculties 

 which guide them in their choice; namely, taste 

 and smell. Lastly, the absorption of the truly 

 nutritious matter is accomplished from their 

 interior, the crude material assumed as food 

 having been first prepared by elaboration in a 

 cavity called a stomach. 



As organized living beings, the soundest 

 philosophy and best ordered experiments lead 

 us to infer that there is little if anything me- 

 chanical in the mode in which either vegetables 

 or animals absorb nutriment. The absorption 

 of their aliment by vegetables is influenced by 

 the seasons, their state of health or disease, 

 their age, and external circumstances gene- 

 rally, the temperature, state of dryness or 

 moisture, &c. of the air with which they are 

 surrounded ; the cause of the absorption of 

 their food by vegetables is, therefore, some- 

 thing different from what is called capil'ary 

 attraction, or the law by which fluids ascend 

 in tubes of small calibre. 



The proper passage of the nutriment into the 

 bodies of animals occurs from their interiors, 

 and in a very large proportion (probably in 

 every somewhat perfect member) of the class, 

 by means of a special set of vessels denomi- 

 nated lacteals or lymphatics, no system cor- 

 responding to which exists among vegetables. 



The very lowest tribes of the animal king- 

 dom, the entozoa, acalephse, polypi, &c. having 

 no proper vessels of any kind, the cellular 

 membrane of which they consist absorbs, and 

 by virtue of a peculiar vital process, distributes 

 the nutritive juices extracted from the matters 

 received into the stomach and alimentary canal 

 to all parts of their bodies. Those tribes of 

 animals which have naked skins have the faculty 

 of absorbing by their exterior also. 



Still less than in vegetables, can we suppose 

 that the process by which in animals nutriment 

 is ultimately absorbed into the body, whether 

 from the exterior or the interior, is akin to 

 mechanical or capillary attraction. The tissues 

 of which animal bodies consist are, indeed, 

 permeable to fluids, but this does not explain 

 the collection of these fluids in so many tribes 

 into particular canals, and still less does it 

 solve the problem of the continued motion 

 onwards in determinate directions within these 

 channels. 



Absorption of alimentary and other matters, 

 therefore, in both of the grand divisions of the 

 organized world, must be held as a vital act, 

 as one of the particular laws superadded in 

 organized beings to the general system of phy- 

 sico-chemical ordinances that-mle the universe 

 and its parts. This quality is common to 

 vegetables and animals. 



By far the greater number of animals have 

 one or more special openings, a mouth or 

 mouths, by which they take in such sub- 

 stances as are fitted for their nourishment. 

 Even the greater number of animals as low in 

 the scale as the infusoria, have been recently 

 demonstrated (by Ehrenberg) to be provided 

 with an opening of this kind. Several, how- 

 ever, seem to receive aliment by the way of 



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