520 



MUSCULAR MOTION. 



experiments of Miiller, Valentin, and others, 

 to be erroneous and unworthy of credit. But 

 I have elsewhere* adduced the evidence of 

 direct microscopical observations made on living 

 fragments of the elementary fibre of voluntary 

 muscle, entirely isolated from every extraneous 

 tissue, whether nerve or vessel, to shew that 

 this is a property inherent in this tissue, and 

 that, whatever be its source, it is capable of 

 being brought into action by a stimulus topi- 

 cally applied. Thus, when such a fragment is 

 examined, contraction is found to occur first 

 at its broken extremities, and if svater (which 

 has long been known to be a rapid exhauster 

 of muscular irritability) be brought into con- 

 tact with it, it is seen to absorb the fluid 

 and to be excited to contractions, which com- 

 mence at the surface. The same thing is fre- 

 quently to be met with under a different form. 

 A particle of foreign matter, as a hair or piece 

 of dust, may be included by design or accident 

 in the field so as to touch the side of the fibre 

 at a single point. When this happens, the fibre 

 will often exhibit a contraction so plain and so 

 limited to the point touched, as to give un- 

 equivocal proof of its being the result of the 

 irritation of pressure. 



Theseinteresting phenomena maybe observed 

 more or less satisfactorily in all animals whose 

 fibres retain their irritability for a sufficient 

 length of time after removal from the body, 

 and the crab and lobster will be found the most 

 favourably adapted for the purpose. In many 

 reptiles and fishes, also, the steps occur slowly 

 enough to be adequately scrutinized. 



The facts in question can admit only of one 

 explanation if it be conceded that the mus- 

 cular element has been here separated from 

 the nervous ; and certainly that separation 

 has been effected unless the nervous tubules 

 send off from their terminal loops a set of 

 fibrils which penetrate the sarcolemma and 

 diffuse themselves through the contractile ma- 

 terial within ; a supposition for which there 

 exists at present no foundation in the obser- 

 vations of the most diligent investigators of 

 this subject. 



They will, therefore, probably, be regarded 

 as conclusive proof that contractility is a pro- 

 perty inherent in the very structure of muscle, 

 and capable of being excited to action inde- 

 pendently of the immediate instrumentality of 

 nerves. 



The determination of this point must have 

 a very important bearing on the question of 

 the nature and cause of contraction, into which 

 no small confusion has been introduced by 

 the attempts to account for that phenomenon 

 by various hypotheses of electrical action. That 

 one, especially, which aims at establishing an 

 attraction between distant points of the fibres 

 where the nerve crosses them, (the ' zig-zag 

 hypothesis' of Prevost and Dumas,) and which, 

 with the wrongly interpreted facts on which it 

 principally rests, has had an immense, though 

 sometimes unperceived influence, ever since it 

 was broached, on the whole question of con- 

 traction, is entirely refuted by the facts above- 



Phil. Trans, 1840, p. 487. 



mentioned. There are some others, sprung out 

 of this, which do not here require more than a. 

 passing allusion. 



2. Source of contractility : whence derived 1 

 This important question, like the last, is de- 

 bated up to the present day, but seems at 

 length to have become disenthralled of certain 

 loose hypotheses which have long interfered 

 with its settlement. The discussion may be 

 limited to such particulars as seem to be the 

 most conclusive. 



It may be observed that the contractility and 

 development of muscle, other things being the 

 same, are always proportionate to one another. 

 All causes interfering vvithdevelopmentdiminish 

 contractility. Thus muscles become atrophied 

 and weak by disuse, by lessening their supply 

 of blood, by cutting off their connexion with 

 the central part of the nervous system. They 

 are, on the contrary, augmented both in size 

 and power by active use, during which both 

 the vascular and nervous parts supplied to them 

 are no doubt urged to increased activity. How 

 is it to be decided whether these changes of 

 contractility depend on changes of nutrition, 

 or whether both be not a common result of 

 changes in the amount of nervous power brought 

 to act upon the muscles. Dr. Marshall Ilall 

 has remarked that in paralysis from disease 

 involving the spinal cord or nerves, the wasting 

 of the muscles is far more rapid and complete 

 than in paralysis from affection of the brain, 

 wherein the spinal cord and its connection with 

 the muscles remains in a normal state; and the 

 deduction seems at first sight plain and inevit- 

 able, that it is from the spinal cord that the 

 contractility is derived, or at least that the 

 integrity of the spinal system is essential to the 

 maintenance of that property in the muscles. 

 An ingenious experiment of Dr. John Reid's,* 

 however, proves that this is not the case, and 

 explains the part which the spinal system plays 

 in respect of this property in the instances 

 referred to. " The spinal nerves were cut 

 across, as they lie in the lower part of the 

 spinal canal, in four frogs, and both posterior 

 extremities were thus insulated from their ner- 

 vous connexions with the spinal cord. The 

 muscles of one of the paralyzed limbs were 

 daily exercised by a weak galvanic battery, 

 while the muscles of the other limb were 

 allowed to remain quiescent. This was con- 

 tinued for two months, and at the end of that 

 time the muscles of the exercised limb retained 

 their original size and firmness and contracted 

 vigorously, while those of the quiescent limb 

 had shrunk to at least one-half of their former 

 bulk, and presented a marked contrast with 

 those of the exercised limb. The muscles of 

 the quiescent limb still retained their contrac- 

 tility, even at the end of two months ; but 

 there can be little doubt (adds Dr. Reid) that 

 from the imperfect nutrition of the muscles 

 and the progressing changes in their physical 

 structure, this would in no long time have dis- 

 appeared had circumstances permitted me to 

 prolong the experiment." It is clear from this 



* Edinb. Monthly Journal of Medical Science, 

 May 1841, p. 327. 



