NE 



S AND \ER\'OUSNESS 



DAVID FRASER HARRIS. ^[.D.. B.Sc. (LoxD.) 



^Lecturer t>ii l'hy.^i<)h)i>y. I'liii'crsity of lUinmt^haiii.) 



iCoiitinucd fruiii pci^^c 22.) 



The answer to-day to our question is that we do 

 know something of the material hasis of nerve 

 energy, although only a few \ears ago we should 

 h" , e had to confess complete ignorance, ^^'e helieve 

 '.; to be related to microscopic granules named after 

 a German neurologist. Xissl. These granules of 

 Nissl are known to break up in cells that are 

 fatigued, luu to be reformed when the cells have 

 rested, so that we infer they are connected with 

 the output of energy. In various mental diseases 

 they are altered, also in alcoholic poisoning : the 

 brain is never in good health if these granules are not 

 of normal aspect. It is these granules which contain 

 a high jiercentage of phosphorus. Long before the\- 

 were discovered it was known that nerve-matter 

 [)ossessed much phosphorus, and hence arose the 

 popular notion that to gain nerve-strength one ought 

 to eat foods containing much phosphorus — fish and 

 animals" brains for instance. Now while it ma\- be 

 good to eat fish and brains, the notion underhing 

 the practice is based on the fallacy that we 

 can increase the amount of an\- element in the 

 tissues provided we eat food containing much 

 of it. But the fact is we cannot in this wa\- over- 

 saturate the tissues with any given element : the 

 tissues can absorb (assimilate) only a certain 

 quantity of it, corresponding to their particular 

 chemical affinity for the substance in question. In 

 conditions of health this affinitv limit cannot be 

 exceeded, but it is otherwise in cases of patho- 

 logical deficienc\- of the element in question. For 

 instance, a healthy man bv taking a great deal of iron 

 in his diet w ill not cause a greater quantity of it than 

 normal to be retained by his tissues : but the case of 

 a person who has not been absorbing enough iron is 

 quite different. If now capable of absorbing it, he 

 may, by taking foods rich in iron, bring uji the iron- 

 content of his tissues to the normal but not bevond 

 it. The case of phosphorus is similar. If for any 

 reason the central nervous s\stem has been starved 

 of phosphorus, then food containing it ma\' be gi\en 

 with advantage, but the phosphorus-content of the 

 brain cannot be raised above the normal. Wastiup 

 diseases of the central nervous system certainh- 

 involve loss of this element which ought to be 

 compensated for. The same reasoning applies to 

 phosi)hatic tonics. They may benefit the l)od\- in 



certain wavs. but thev cannot become the means of 

 increasing the percentage of phosphorus beyond its 

 normal in the ner\'e-tissues. 



We mav now ask ourselves what is it that keeps 

 up the continual outflow of impulses from the centres 

 to the peripher\- ? The answer is that this energy is 

 liberated in the special granules already alluded to 

 bv the inpouring of afferent impulses constanth' 

 arriving at the centres of the nervous system. 

 When one thinks carefully about it one sees that a 

 vast number of all sorts of impulses must be pouring 

 into the nervous centres both from all the sense- 

 organs as well as from the internal organs. Sensory 

 impressions from the organs of vision, hearing, smell, 

 taste and from the skin — those of contact, pressure, 

 heat and cold — and others of a less well defined 

 nature from internal organs are continually arriving 

 at the ner\ous s\-stem. Painful impulses are from 

 time to time also coming in. ^^'e are not, of course, 

 conscious of a tenth part of all these, but they are 

 pouring in ne\ertlieless ; some of them even in sleep, 

 when those from the skin and internal organs are 

 still entering the ner\ous system. The nervous 

 svstem is never without some incoming impulses, 

 and we are powerless to prevent the entrance of the 

 \ast majoritx- of them. Just as the hum or roar of 

 the traffic of a great city pours into the room 

 when the window is opened, so do the afferent 

 neural impulses pour into the brain and spinal cord. 

 The general tendency for these impulses is to cause 

 the nerve-centres to "discharge : that all the centres 

 are not simultaneously discharged is due to a large 

 number of cooperant conditions. Some impulses 

 ma\- be too feeble to arouse the first centre 

 encountered, as when the fl\- is not felt until it has 

 stung vou : but a series of such too feeble impulses 

 mav, bv being summated, effect what no one of the 

 series is able to do. Or. again, two impulses may 

 meet and interfere with each other in such a way 

 that no action is aroused, just as when two sound- 

 waves meet in a particular fashion and give rise 

 to silence, or two colour-waves to blackness. This 

 last case is one of "inhibition by interference" of 

 neural currents. 



There is no doubt that the -general incoming 

 neural " hum " goes to produce those outflowing 

 currents which maiiitaui the unconscious general 



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