February, 1911. 



KNOWLEDGE. 



61 



tissue-tone. In proportion as we cut off the 

 multitude of incoming impulses so tone vanishes ; as, 

 for instance, in sleep, in which no impulses are coming 

 in from the higher sense-organs, and therefore the 

 centres for tone to a large extent are unstimulated. 



Keeping animals in the dark and in silence lowers 

 their tone : cows kept in dark byres secrete poorer milk 

 than those in well lighted ones. This is due to the 

 depressed chemical tone of the cells of the mammar\- 

 gland. It has beeii experimentally proved that if the 

 afferent nerves from a limb are cut, the muscles of 

 the limb suffer diminution of tone. It is evident, there- 

 fore, that the afferent nerves and the efferent nerves 

 are functionalK" verv closely related through the 

 intermediation of their common centre. The entire 

 nerve-path from the periphery, up the afferent nerve 

 through the centre and down the efferent nerve is 

 known as the " reflex nerve-arc." A vast number of 

 the functional units of the central nervous s\'stem 

 can be looked upon as reflex or " sensori-motor " 

 nerve-arcs. These arcs are continualh' recei\ing 

 impulses one wav, and sending them out the other 

 wav. that is transmitting them in one fixed direction 

 onh'. The impulses which go out are not identical 

 w ith those that come in : in many cases, although 

 thev come in continuously, thevgo out intermittenth- 

 bv special rhvthms of their own. 



Now the intensitv of the response given by a 

 centre depends upon two things — first the intensitx' 

 of the incoming impulse, and secondK' its own 

 condition of being affected b\' the stimulus easily 

 or the reverse ( Affectabilit\'). This a[)plies to all 

 centres, whether those in the cord unrelated to 

 consciousness, or those in the brain related to 

 perceptions, emotions, ideas and the will. Now- 

 one form of ner\-ousness is that associated with an 

 abnormalh' violent response to a stimulus. This 

 form of nervousness is that of the " nervous tempera- 

 ment " as opposed to the j)hlegmatic, for there is 

 more than a grain of truth in the old classification 

 into h-mphatic or phlegmatic, nervous, sanguine and 

 melancholic temperaments. The nervous tempera- 

 ment has in recent times mereh' been rechristened 

 " neurotic."" A neurotic person is one whose nerve- 

 centres are, as compared with those of the majority 

 of people, undul\- aflectable. This condition of 

 undue affectabilit\' manifests itself in nuin\' \er\' 

 different ways. If a hundred people are in a hall 

 and a door bangs loudlw three of them iiia\' jump 

 up from their seats while the other ninety-seven 

 mereh- turn their heads in the direction of the 

 sound : tlie three would be for the compan\- in 

 question the representatives of the neurotic con- 

 stitution. The physical intensity of the stimulus 

 was presumably the same for the whole hundred, 

 but it produced a greater effect on three of them 

 because their nerve-centres were in a state of 

 excitability greater than the average for the particular 

 company in the room at the time. Again let us 

 suppose a hundred people come into a place where 

 there is a large bowl of powerfullv perfumed roses : 

 ninet}-seven appear indifferent and settle down to 



various occupations: one is visibly delighted with the 

 odour: 2 second says, "That is a smell I detest," 

 while tl J third gets an attack of asthma. The last 

 three are " nervous '" as regards the neural average of 

 the assemblv . Their nervous systems are unduly 

 affected by tli perfume of rose; • the form it 

 takes in one distinct aesthetic pleasure, in a 

 second well-mark. .1 aesthetic pain, in z. third it gives 

 rise to a motor effect, a spasm of the muscles of the 

 lironchial tubes. This last is known as ar. s.-^itack of 

 asthma ; it belongs to a class of conditions called 

 neuroses. Neurotic people exhibit neuroses. A 

 neurosis is an excited or excitable state 01 some 

 centre or centres of the nervous system expressing 

 itself in an outflow of nerve-energ\- into such channels 

 as injurioush' aftect certain organs or tissues. 

 Nervous attacks or " attacks of nerves " may be 

 taken as the popular s\'nonyms for neuroses — fits 

 of trembling, limbs shaking, "'the ([uivering like 

 an as[)en leaf "' of the novelette, palpitation and 

 other visible effects of fear on the approach of an 

 ordeal ("stage-fright,"" examination fright), blushing, 

 blanching, perspiring, ililataticm of the pupil, and in 

 some cases even vomiting, all well-known results of 

 stimulation of lower centres acted on by impulses de- 

 scending from higher ones. Popularly the '" nervous"" 

 person is the one who blushes, pales or perspires too 

 easiK'. whose centres for these expressions of 

 emotion are abnormalh' aftectable and are set in 

 motion hv conditions which would ha\'e little or no 

 eft'ect on a person perfectly normal as regards the 

 nervous system, a person with what is called a 

 ■■ well-balanced nervous system."" What, however, 

 is the cause of the abnormal aft'ectability of the 

 centres in a nervous person it would be difficult to 

 sa\'. In many cases it is probably due to malnu- 

 trition of the centres. Nerve substance is chemically 

 only a ver\- complicated form of fat, and fat people 

 are almost ne\'er neurotic. We must not jump to 

 the conclusion that because a person is fat his 

 nerve-centres are of necessity well nourished, though 

 thev usualh- are. There are various kinds of obesity, 

 some not indicating good nourishment ; but as a 

 rule it is lean people who are nervous. This is, of 

 course, what Shakespeare alludes to when he makes 

 Caesar say — 



" Let me have men about me that are fat ; 

 Sleek-headed men and such as sleep o' nights : 

 Yond' Cassius has a lean and hungry look : 

 He thinks too much : such men are dangerous." 



Of course we must distinguish between the thin, 

 pale, neurotic person, and the thin. " wiry," fit 

 person whose nerve-centres may indeed be aff'ectable 

 without being abnormalh" or weakly affectable. For 

 there is the healthy, robust nervous system with 

 plenty of nerve-energy able to be discharged, and 

 there" is the weakly, excitable system with little 

 energy alwa\-s tending to leak away. The two 

 conditions are quite different. The ease of response 

 to a stimulus is one thing, the amount of energy 

 liberated by a stimulus quite another thing. The 

 same amount of pull will fire oft' a pop-gun 



