ANIMAL

(Lat. anima, soul, or life.) The name of the higher division or kingdom of organised beings, distinguished by endowments of sensation and voluntary motion, super-added to the organic functions which animals po e in common with plants. It has been objected to this definition, that the so-called sensitive plant is susceptible of impre ions which cauge action and motion of its parts, and that the embryos of Algae and Confervse have locomotion, while many of the lower animals are fixed as immoveably to the earth as plants. But these objections have no real value; and could only have arisen from confounding irritability with sensation, which are two very different phenomena. It is the property of all living organised beings, and e ential to their existence as such, to be susceptible of the impre ions of certain stimuli, which occasion a reaction of the part stimulated;and the main object of physiology is to determine the precise mode in which each organ ofa plant or animal reacts when stimulated. But it is here only nece ary to state, that the muscular fibre in animals reacts when stimulated by an angular puckering called contraction, and this property is termed irritability. It is independent of the nerves and of sensation, for a portion of muscle removed from an animal body manifests the same contraction when irritated, whether mechanically, galvanically, or chemically. In the living animal the most common stimulus of the muscular contraction is the operation of the nerves, excited by the will, and is commonly the consequence of an act of sensation; but this is by no means the only stimulus by which the irritable property of the muscle is or can be called into play. In plants, universally, there are also irritable parts, or parts which react when stimulated by producing motion of a part or the whole of the body. It is this property which occasions the motion of the cambium or sap; it is by the same endowment that growing plants incline to the light, and extend their roots to the most congenial soil; or entwine their tendrils around the bodies which serve as their support; or move the stamens in regular succe ion towards the female part or pistil (saxifrage), or incline the pistil succe ively to each stamen (lily). By a modification of the same irritable property, some plants close their leaflets or flowers at sunset; while others, like the nocturnal animals, go to sleep, as it were, at the approach of day. By a higher degree of this Irritability the leaflets of the fly-trap (Dioncea) approximate each other, and inclose the irritating insect which has alighted upon them; and the Mimosa pudic a withdraws its leaves from the offending touch;— while the Desmodinm exhibits during the day a constant alternate movement of the le er folioles, analogous to the quicker vibration of the cilia [s. 66]