22 



KNOWLEDGE. 



January. T)11. 



have not forgotten about him, that messages have 

 been duly sent out to order his food to be brought 

 into camp, that orders have been recei\'ed as to how 

 each minute of his day is to be occupied, and so on. 

 A command to action imparts no strength to act, but 

 it constitutes a necessary antecedent condition for 

 an attentive, well drilled soldier to obe\' on the 

 shortest notice in the best possible manner. This is 

 w hat tone does for muscles ; it keeps them readw 

 This outflow of what we may convenienth- call tonic 

 impulses has nothing to do with our consciousness : 

 although diminished in intensity, for instance, during 

 sleep, it is not abolished. We do not therefore 

 consciously or voluntarily innervate our muscles : 

 they are innervated subconscioush'. When the 

 nervous s\-stem dies the muscles take on the flaccidit\- 

 of death before they enter upon /-/^'o/' iiiorfis, the 

 rigidit\' of death. 



Now we have a good deal of e\idence that the 

 outflow of these tonic impulses is rlnthmic or 

 intermittent, in other words at a certain regular rate 

 per second. Physiologists are not agreed as to the 

 exact rate of arrival of these at the muscle, but efforts 

 are being made to determine it. In what we call a 

 voluntary muscular contraction it is e.xtremeh' 

 probable that, although the intensit\- of these impulses 

 is very greatly increased, their number per second, or 

 periodicity, remains the same. The will, then, onh- 

 exaggerates the existing state of tone; this exaggerated 

 tone is a voluntar\- contraction, and hence it is 

 sometimes said that '" tone is incipient contraction " 

 — a very good description. We know that heat is 

 given out in voluntary contraction, but heat is also 

 produced by a muscle in tone : and in [)roportion as 

 the tone dies down so is the output of heat 

 diminished. 



This unconsciously exerted tonic influence of the 

 nervous centres on the muscles is, like man\- other 

 things, best realised when it is temporarih- diminished 

 or done away with. Thus, when a man gets a blow- 

 on the head, is " stunned." or suffers a severe and 

 especially sudden injury, or has his central nervous 

 s}-stem badly poisoned b\- alcohol or chloroform, 

 he is quite unable to remain in a standing posture. 

 This shock, or collapse, is due to his muscles having 

 become more or less toneless, not so much because 

 the\- are poisoned as because their innervation is 

 reduced or abolished through the mechanical or 

 chemical damage to the centres emitting the tone- 

 maintaining impulses. The nerve-cells responsible 

 for sending out these tone-preserving impulses are 

 sometimes called " trophic centres," or centres related 

 to trophism, a Greek word meaning "growth" but 

 now taken as synonymous with tissue-health. Trophic 

 nerves for muscles are none other than the efferent 

 nerves conveying impulses inducing tone in the 

 muscles. Trophic impulses in any other sense, in so 

 far as muscles are concerned, do not exist. 



All tissues, even such an apparently lifeless one 

 as bone (which, how^ever, is very much alive), when 

 from any cause deprived of their nerve-suppl\- suffer 



in health, become atrophic, or atrojihy. It is equal!}' 

 correct to speak of blood-vessels and glands as being 

 kept in tone or in a good trophic state by reason of 

 their innervation. Thus, if the efferent nerve to an\- 

 tissue is cut. the tone of that tissue is diminished or 

 abolished for the time being, muscles become flabbv, 

 blood-vessels parah-sed or dilated, and glands quite 

 unhealth^•. It will be convenient to ha\'e a term for 

 the nerve-cell in the centre and its outgrowth, the 

 efferent nerve-fibre, which passes all the wa\' from 

 the central nervous centre to the periphery : it is 

 " the efferent neurone." Neurone means nerve-cell 

 and all its processes including the long conducting 

 process to the tissue or organ innervated. The 

 nerve-fibres which stretch from nerve-cells to tissues 

 have at least the propertv of conductivitv, the power 

 of conducting nerve-impulses. Toneless muscles are 

 a sign of deficient innervation, a condition seen for 

 instance typicalh' in melancholia. It is, of course, a 

 mental condition, but its outward and visible sign is 

 deficiencv of tone of all tissues not only muscles but 

 blood-vessels, glands, and skin as well. Deficient 

 innervation leads to deficient tone, whether that 

 deficient innervation is due to mechanical injury to 

 the nerve or to a depression of the emitting centre 

 itself. In neurasthenia, again. inner\'ation is deficient; 

 not onh' are the muscles lacking in tone, but the 

 glands, for instance the gastric glands, are deficient 

 in chemical tone, and as they do not secrete sufficient 

 h\'drochloric acid there results the consequent ner\'ous 

 d\'spepsia. Popularlv a neurasthenic is " a nervous 

 person"; stricth' speaking such a person is suffering 

 from weakness of the nerve-centres, probably due to 

 their being poisoned or not sufficiently nourished at 

 some previous time. Nerve-centres themselves, then, 

 can be in good health, full of vigour and nerve-energy, 

 or the\' can be less vigorous, putting forth less 

 energ\'. be definitely weak. Neurasthenia is onh- 

 Greek for ii(>t-sfren}>tli of nerx'es : but in this case 

 " ner\'es " means nerve-centres, since ner\'e-trunks 

 are not sources of energy and merely conduct 

 impulses. Nerve-energy or nerxous energy are terms 

 one reads about a great deal, sees very often used in 

 advertisements of quack niedicines, and so on; but it 

 is a thing of which the man of science has very little 

 knowledge. There must, of course, be such a thing as 

 nerve-energ\' ; else nerve-centres could effect nothing 

 and affect nobod\', for "ex iiihilo iiiliil fit." The 

 English physiological psychologist. Dr. MacDougal 

 of Oxford, has coined the word " neurine " as a 

 convenient term for nerve-force. Although we know- 

 almost nothing about nerve-force we know a little of 

 what it can do. just as, although we do not know- 

 much about electricity, we know something of what 

 it can do: both electricity and neurine pass from 

 places of high to places of lower pressure. Returning 

 to the centres in the spinal cord, we see that they 

 are the sources of the nerve-energy sent out to the 

 tissues everywhere; but we might at this point ask 

 ourselves: do we know anything of the material basis 



of this ner\'e-energy .'' 

 ( To l>c continued I. 



