ACTION OF ANIMALS. 



31 



and chemistry in matter not animated, it must not be 

 understood that these lavs ;irc violated, or that the 

 properties of matter arc, in the least, either changed 

 or destroyed. If creation were thus unstable, it could 

 not endure : if the properties of matter, which belong 

 to it simply as such, and without any reference to 

 composition or combination, were not co-existent with 

 matter, inseparable from it for an instant, and capable 

 of perishing only with its final destruction, there would 

 hi: an end not only of all knowledge of matter, but of all 

 matter to be known ; for, other than by its properties, 

 we do not, and we cannot, know any thing of matter. 

 But the changes, whether the chemical ones of com- 

 bination, or the mechanical ones of place, are open to 

 our observation, and an endless variety of them is per- 

 fectly consistent with perfect sameness in the proper- 

 ties of matter abstractedly considered. The same 

 particle of carbon, for instance, may be at first a dia- 

 mond, may pass in succession through every animal 

 and every vegetable, and every mineral, that can con- 

 tain carbon in its composition, may travel millions of 

 times round the globe in the course of its varied com- 

 binations, yet maintain its perfect identity of essence 

 and qualities all the time, and return to a diamond at 

 last. That principle is true, not only in the case of 

 animal action, but in that of all action among matter, 

 whatever we may suppose, to be its cause ; and there- 

 fore it is of the utmost, importance that respecting it 

 our perception should be clear and our understanding 

 sound. Having noticed it, and it is one of those sub- 

 jects which should frequently be repeated as a pre- 

 face, we shall very shortly advert to the general prin- 

 ciple of mechanical action in animals. Their actions 

 are all motions, or the results of motions of some sort 

 or other, or they are active resistances to external 

 motions, which, in principle, amount to very nearly 

 the same. If in one instance an eagle cleaves the 

 still air at the rate of fifty miles an hour, and in ano- 

 ther it maintains its perch on the pinnacle of the rock, 

 while the tempest sweeps around it with the same velo- 

 city ; or if in one ease a fish darts through the stilly 

 pool with any degree of rapidity, and in another keeps 

 its place in a current which is racing onward just as 

 fast; the mode of action maj be different, but the 

 intensity, or, as we may call it, the quantity of action, 

 is the same in both : but, in judging of these actions, 

 we must, bear in mind that there is one element of 

 which we are very ignorant the energy of the 

 animal. That is not in proportion to the mass ; for if 

 man had the energy of the ant, he could walkover a 

 city in a straight line, without needing the buildings 

 in his way ; and if an elephant had, bulk for bulk, the 

 same energy as a flea, it could clear London at a 

 single bound. 



The action of all anima's may be said to be the 

 result of muscular energy, though the effect of the 

 muscular exertion is, sometimes, increased by struc- 

 tural means. Thus, when the tendon of a muscle 

 passes over the processes of a joint, the tendon is as 

 much pulled by bending the joint the other way, as 

 it would be by the action of the muscle. By that 

 species of action all birds maintain their footing, all 

 perching birds their perch, and birds which kill their 

 prey by clutching or trussing it against the ground 

 give effect to their talons. All animals, indeed, can 

 give different degrees of stability to their feet, by dif- 

 ferent bendings of the limbs; and these flexures are 

 not so much shillings of the centre of gravity, as of 

 the part of the base on which the chief pressure rests, 



though, if the object be mere stability, the centre of 

 gravity is speedily shifted by other flexures, so as to 

 bring the pressure equally upon all parts of the base, 

 and of course neatest to that part which is in the state 

 of greatest tension and best capable of resisting. 

 Bending the knee, or, which is the same in effect, 

 bending the ankle joint, pulls the great tendon of the 

 heel, as forcibly as it could be done by the contraction 

 of the muscles of the calf. If it be done suddenly by 

 a blow behind, when the body is in a very erect po- 

 sition, and the weight chiefly on the heels, the sudden 

 pressure on the balls of the feet in advance of the 

 centre of gravity is very apt to throw the body flat 

 on the back ; but in leaping, when the body is bent 

 forward on the hip joints, the very same position of 

 the leg throws it upward and forward when the leap is 

 taken. 



Animals which repose on the feet do it, not by 

 muscular exertion, for that is inconsistent with repose 

 they do it by this adjustment of tension upon the 

 tendons; and if it is against, a current, by adjusting 

 the body to that current. When a man stands with 

 his face to the wind he must bend so far forward as 

 to advance the centre of gravity, till the tendency he 

 would have to fall if the wind were not blowing be 

 equal to the force of the wind ; and if he stand with his 

 back to the wind, he must lean as far backward. A 

 man has, however, less command of himself with the 

 wind in his back than in his face, just as he has more 

 command of himself in climbing a hill than in 

 descending one; and the cause is, that in facing the 

 wind and in ascending, the tendon alone brings the 

 ball of the foot into action, and there are the muscles 

 of the calf to assist ; whereas, in the other cases, the 

 muscles are always in action, and the muscular energy 

 wears out. 



Quadrupeds for the most part repose prostrate ; 

 but it will be found that all those which repose on the 

 bended legs repose on them so that the tendons are 

 stretched, and will assist as a spring in rising. That 

 is remarkable in the couchant attitude of some of the 

 dog tribe, more especially in greyhounds, and also in 

 cats preparatory to taking their spring a position in 

 which we may conclude that both muscles and 

 tendons are in that state in which they can act most 

 simultaneously and with the greatest energy. 



The positions of birds when perched are well 

 worthy of attention, as they show the perfect state of 

 " preparation for action," in which all living creatures 

 in a state of nature are, when they are at rest, so that 

 in case of surprise they are never taken unawares, or 

 at a disadvantage. Birds on their perch always face the 

 wind ; and though many of them " give themselves to," 

 or "turn down'' the wind, especially in attempting 

 their escape from rapacious birds, which have not that 

 habit, they all rise with their heads to the wind, and 

 when they " turn down," it is by an oblique posture of 

 the body, and an oblique lateral motion. If a bird 

 were to perch with its tail to the wind, there would be 

 two tendencies to drive it from its perch : the wind 

 would, by turning the feathers, and even getting under 

 the wings, have great power over it ; and the action 

 of that power would unbend the legs, and thereby 

 loosen the feet from the perch. But perching with the 

 head to the wind, the bird is enabled to make the wind 

 itself a means of stability. The usual position of repose 

 in a calm in perching birds, is not any effort to keep 

 the perch. It is done simply by the adhesion which 

 results from gravitation, and that too without moving 



