PHYSIOLOGY OF THE NERVOUS SYSTEM. 



72 IM 



non, but is chiefly due to a change in the 

 circulation of the penis, to an increased attrac- 

 tion of blood to the organ in virtue of the 

 inflammatory state. 



Enough has been said to shew that, to lay it 

 down that every act of ingestion, of retention, 

 of expulsion, and of exclusion, is a reflex act, 

 is opposed to all that we know of the intimate 

 nature of these actions. The power resident, 

 not in the spinal cord only, but in every ner- 

 vous centre in which nerves are implanted, 

 whereby, to use Prochaska's words, sensory 

 impressions may be converted into motor im- 

 pulses, is no doubt of immense importance to 

 the animal economy; but Dr. M. Hall has 

 been evidently led, by an imperfect analysis of 

 the functions we have been considering, to 

 assign to this power too large an influence in 

 them ; and on the other hand, he has over- 

 looked its obvious and important influence in 

 other phenomena. 



Dr. Marshall Hall also attributes to the spinal 

 cord a direct action or influence which mani- 

 fests itself, first, in the tone, and secondly, in 

 the irritability of the muscular system. 



I regret to be compelled to differ again from 

 Dr. Hall with respect to this point, and to 

 express my opinion that this dogma is incon- 

 sistent with established doctnnes of physiology. 



By the tone of the muscular system, I un- 

 derstand that state of passive contraction which 

 every healthy muscle exhibits when not in active 

 contraction. It is this state which gives the firm, 

 resisting, resilient feel, which the physician 

 knows to be characteristic of a healthy state of 

 the muscle. By virtue of it a muscle can 

 adapt itself to changes which may take place 

 in the distance between its two points of attach- 

 ment; and it is in virtue of this property that 

 a muscle shortens itself when the stretching 

 force of its antagonist has been removed. 

 When the muscles of one side of the face have 

 been paralysed for some short time, the features 

 lose their balance, because the muscles of the 

 sound side have contracted to within a smaller 

 space, having lost the resistance of those of the 

 opposite side. It is equality of tone which 

 preserves the equilibrium between symmetrical 

 muscles; it is tone or passive contraction 

 which keeps hollow muscles quite closed, if 

 they are empty, or firmly contracted on their 

 contents, if not so, as the heart and intestine ; 

 the tone of the predominant flexor muscles 

 keeps limbs, whilst at perfect rest, in a semi- 

 flexed position ; it is tone which keeps sphinc- 

 ter muscles in a closed state. 



The question is, do the muscles derive their 

 state of tone from the spinal cord, and is this 

 property dependent on that organ ? 



This question is answered in the negative, if 

 we can shew that there are good and sufficient 

 grounds for affirming that muscles possess 

 within themselves all the conditions necessary 

 for the generation of their proper force. That 

 muscles do enjoy these conditions is manifest 

 from the following considerations: 1. their 

 peculiar chemical composition, their main con- 

 stituent being Jibrine, a substance which, we 

 know from the phenomena of the coagulation 



of the blood, exhibits a remarkable tendency 

 to contract; 2. their anatomical constitution; 

 the arrangement in fibres, the intimate texture 

 of those fibres, which in the muscles of the 

 greatest power, the voluntary muscles, is highly 

 complicated ; 3. from the large quantity of 

 blood sent to muscles, which are probably more 

 freely supplied with that fluid than any other 

 texture in the body, and which receive it in the 

 greater quantity when that contractile power is 

 more active; 4. from the fact pointed out by 

 Mr. Bowman, that a single muscular fibre, en- 

 tirely deprived of all nerves, may be made to 

 contract by a slight stimulus applied to any 

 part of it; 5. from the knowledge which we 

 now possess that the mechanism of these ac- 

 tions may be seen by the microscope even in 

 detached portions of muscular fibres ; 6. from 

 the fact that muscles dissociated from the ner- 

 vous centres by the section of all the nerves 

 distributed to them, retain their power of con- 

 traction for a very considerable period, long 

 after the nerves which sink into them have lost 

 their excitability. 



All these points afford the highest degree of 

 probability that there is no direct dependence 

 of muscle upon the nervous centres for the 

 developement of its proper force ; and that this 

 force is the result of the nutrient actions of 

 muscle. The only way in which the nervous 

 system can be said to have an influence upon 

 the muscular force is by promoting the actions 

 of the muscles, and thereby their nutrition. If 

 a muscle have its nerves divided, and be left to 

 itself, its nutrition fails after a certain period, 

 and its contractility with it ; but if it be exer- 

 cised daily by galvanic stimulation, its nutri- 

 tion remains unimpaired, and its contractility 

 likewise. 



The tone of a muscle is nothing but the 

 effect of the continuous developement of the 

 muscular force resulting from the natural 

 changes in the muscle ; it is this state of ten- 

 sion which denotes that these changes are 

 actively proceeding, and that a uniform degree 

 of attraction is being exerted between all the 

 parts of the muscular fibre, in a degree propor- 

 tionate to their masses, and that by this the 

 muscles are maintained in a uniform state of 

 tension so long as they are undisturbed by sti- 

 muli conveyed to them through the nervous 

 system, or from some other source. 



It seems, therefore, as reasonable as any pro- 

 position in physiology, to affirm that the passive 

 contraction or tone of muscles is due to a pro- 

 perty inherent in the muscular tissue itself, and 

 dependent solely on its proper nutrition, and 

 that it is not derived from any other tissue. 

 And if this be true, it is clear that the spinal 

 cord cannot be the source of the tone of the 

 muscular system. 



This statement is confirmed by the result of 

 the experiment of removing the whole spinal 

 cord in frogs or other animals. When this has 

 been done, the limbs of the animal fall quite 

 flaccid, the muscles being no longer capable 

 of preserving that degree of active contraction 

 which is necessary to maintain attitude. A 

 decapitated frog will continue in the sitting 



