328 DESIGN IN NATURE 



the blood, which, is regarded as the distending medium, is absent. Similar remarks are to be made of the adult heart. 

 The heart both in the young and adult condition is a master organ ; it is, in a sense, the mainspring of life ; its 

 movements, as explained, being fundamental and inherent, and in no way due to caprice or accident. There is no 

 proof that the normal heart is irritable,^ or that stimulation of any Irind is necessary to its action. 



The modern physiologist pricks or applies electricity to a heart or a muscle which is in a state of quiescence, and 

 gets one or more contractions, and straightway concludes that the stimulation is the sole cavse of the movement. He 

 forgets that the heart can and does contract normally without any stimulus, external or internal. This remark ap- 

 plies to all the hollow muscles. It also applies to all the voluntarjr muscles, as they too are moved from within by 

 the efforts of the will, and as apart from all kinds of external stimulation. 



It is true that a muscle can be made to contract by applying an artificial stimulus to it directly,^ or to a cut 

 motor nerve attached to it. It does not, however, follow that the artificial stimulation produces exactly the same 

 result as the impulse sent out through an uncut motor nerve to the muscle by a nerve centre. In like manner 

 artificial stimulation, at its proximal end, of a cut sensory nerve produces pain, but no one can say that the kind and 

 degree of pain are identical with that produced by contact with a natural object applied to the uncut sensory nerve 

 at its distal end. At best the results obtained by artificial stimulation and section of the motor and sensory nerves 

 are crude imitations of the normal acts, and consequently to be accepted with caution. 



As regards the elasticity of muscle much misconception exists. Elasticity, it is said, only acts when muscles 

 relax, elongate, or dilate ; as a matter of fact, the little elasticity there is comes into play also when muscles contract, 

 shorten, or close. This follows, because elasticity, whatever its amount, is a property of the sarcous elements in 

 which muscular movements begin and terminate. The elastic properties of muscle are, as a rule, greatly overstated. 

 When elasticity is to play an important part in hving structures, the structures are specially modified for the purpose. 

 Thiis in the vorticella a special spiral spring is provided for the retractile or shortening movements of the pedicle or 

 stem. The same is true of the wing of the insect, bird, and bat in flexion. Examples of special elastic tissues are 

 afforded by the inter-vertebral discs or cartilages of the spinal column, the ligamentum nuchas, yellow elastic tissue, &c. 

 The large arteries, which contain no muscular fibres, are highly elastic, but the small arteries provided with muscles 

 are very httle, if at all, elastic. 



Elasticity usually manifests itself by recoil or sudden movements. The sudden movements of muscles, how- 

 ever, do not occur during the elongating or dilating process, when elasticity is said to exert its chief powers, but 

 during the shortening or contractile process, when elasticity is said to be in abeyance. According to prevailing 

 views, the shortening or contractile movements of muscles are vital — the elongating or dilating movements elastic. 

 The elongating movements are said to be mechanical, whereas the shortening, contractile movements are said to be 

 vital. According to my experiments and observations, both movements are vital, elasticity plajdng quite a subor- 

 dinate part, but acting to a trifhng extent in either case. 



But (and this is important) the prevaiUng theory of muscular action is inconsistent. In the case of the hollow 

 viscera — the heart, stomach, rectum, bladder, uterus, &c. — the closing, shortening, centripetal movements are said 

 to be vital and sudden ; whereas the opening, elongating, centrifugal movements are said to be mechanical and slow. 



In the respiratory movements, however, all this is said to be changed. In this case, the opening, elongating, 

 centrifugal movements of the chest are said to be vital and sudden, whereas the closing, shortening, centripetal move- 

 ments are said to be mechanical and slow. These two positions, it will be observed, are diametrically opposed to each 

 other. 



If vital acts are required to close the heart and open the chest, it is abundantly evident that both the closing and 

 opening movements of the heart and chest are vital in their nature, but this is what the theory inconsistently and 

 persistently denies. 



There is no difference as to the manner in which the heart and chest are opened and closed. In both, the 

 opening and closing movements are directly due to vital muscular action. The fact that in the chest the muscles 

 act in conjunction with bones and cartilages does not alter the situation. In either case, the movements begin 

 and terminate in the muscles themselves. If, as happens in the chest, the elasticity of the ribs and cartilages is 

 evoked, the muscles are still the prime movers. Bone and cartilage by themselves can neither originate nor 

 perpetuate movement. 



1 Chauyeaumtroduce,! .™all caoutchouc bags into the hearts of horses without interfering in any way with the nomial action of the heart. 

 This experiment is fatal to the theory that the interior of the heart is irritable, and that the blood causes the movements of the heart 



If, ior example, an irritant be applied to a muscle or muscles in the act of elongating, as in a worm crawling forward, the muscles are taken 

 by surprise, and the forward movement is temporarily suspended. The same thing happens when the tentacles of a snail are being mshed out- 

 wards. The tentacles if toiiohed are immediately retracted. In both cases, however, the advance or forward movements are at once resumed wh™ 

 the irritant is removed and the alarm passes off'. The muscles in such cases assert their double power by well-marked centripetal and cent vifi ™1 

 movements. Muscles, or portions thereof, also withdraw and contract in various parts of the body if the skin covering them be suddenly and 



