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.Even in the most favourable instances, when the stimulation or transsectionhas been entirely successful, we have established but one definite point upon a path of conduction; toascertain its full extent, we should have to make a large number of similar experiments, from the terminalstation in the brain to the point of issue of the appropriate nerves.Such a task holds out absolutely no hope ofaccomplishment, since the isolated stimulation or section of a conduction-path in the interior of the brainpresents insuperable obstacles.There are, therefore, only two problems to which these methods can beapplied with any prospect of success.We may use them to determine the course of conduction in the simplestof the central organs, the myel, and in the direct continuations of the myelic columns, the crura; and we mayuse them to discover the correlation of definite areas of the brain cortex with definite organs upon theperiphery of the body.The answer to the former question has been attempted, for the most part, by isolatedtranssection of the various myelic columns; the answer to the second, by experiments upon the stimulationand extirpation of definitely limited cortical areas.Even with this limitation, however, it is difficult to securevalid results.A stimulation will almost inevitably spread from the point of attack to the surrounding part.CHAPTER V.Course of the Paths of Nervous Conduction 88 Principles of Physiological PsychologyThis objection applies with especial force to the electric current, almost the only form of stimulus whichfulfils the other requirements of physiological experiment, and a stimulus which the physiologist is thereforepractically compelled to employ.The same thing is true of the disturbances consequent upon a division ofsubstance.And if one is at last successful in securing the utmost degree of isolation of experimentalinterference, there will still be many cases in which the interpretation of the resulting phenomena is uncertain.The muscular contraction that follows upon a stimulation may, under certain circumstances, be due to a directexcitation of motor fibres, just as well as to a reaction upon the sense-impressions.And the derangements offunction that appear as a result of transsections and extirpations always require a long period of observationbefore they can be accurately determined.This means that the certainty of the conclusions is, again, verylargely impaired: the disturbances set up as the direct effect of operation for the most part disappear as timegoes on, the explanation being that the principal path is functionally replaced by the secondary paths of whichwe spoke just now.(2) The gaps left in our knowledge by the physiological experiment are largely filled out by anatomicalinvestigation.The anatomist has followed two methods in the prosecution of his task: first, the macroscopicdissection of the hardened organ, and, later, its microscopic reduction to a series of thin sections.Of lateyears, the former of these two methods has fallen into disrepute, on the score that it runs the risk ofsubstituting artificial products of the dissecting scalpel for real fibre-tracts.Carefully applied, however, it is avaluable means of orientation with regard to certain of the wider roads of brain-travel; while its critics areinclined, on their side, to underestimate the danger of error in the interpretation of microscopic appearances.And this danger is the more serious, the farther we are from the actual attainment of the ideal goal of amicroscopic examination of the central organ, its complete reduction to an infinite series of sections ofaccurately known direction.For the rest, microscopical anatomy has been brought in recent times to a highdegree of perfection by the application of the various methods of staining [ Pobierz całość w formacie PDF ]
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.Even in the most favourable instances, when the stimulation or transsectionhas been entirely successful, we have established but one definite point upon a path of conduction; toascertain its full extent, we should have to make a large number of similar experiments, from the terminalstation in the brain to the point of issue of the appropriate nerves.Such a task holds out absolutely no hope ofaccomplishment, since the isolated stimulation or section of a conduction-path in the interior of the brainpresents insuperable obstacles.There are, therefore, only two problems to which these methods can beapplied with any prospect of success.We may use them to determine the course of conduction in the simplestof the central organs, the myel, and in the direct continuations of the myelic columns, the crura; and we mayuse them to discover the correlation of definite areas of the brain cortex with definite organs upon theperiphery of the body.The answer to the former question has been attempted, for the most part, by isolatedtranssection of the various myelic columns; the answer to the second, by experiments upon the stimulationand extirpation of definitely limited cortical areas.Even with this limitation, however, it is difficult to securevalid results.A stimulation will almost inevitably spread from the point of attack to the surrounding part.CHAPTER V.Course of the Paths of Nervous Conduction 88 Principles of Physiological PsychologyThis objection applies with especial force to the electric current, almost the only form of stimulus whichfulfils the other requirements of physiological experiment, and a stimulus which the physiologist is thereforepractically compelled to employ.The same thing is true of the disturbances consequent upon a division ofsubstance.And if one is at last successful in securing the utmost degree of isolation of experimentalinterference, there will still be many cases in which the interpretation of the resulting phenomena is uncertain.The muscular contraction that follows upon a stimulation may, under certain circumstances, be due to a directexcitation of motor fibres, just as well as to a reaction upon the sense-impressions.And the derangements offunction that appear as a result of transsections and extirpations always require a long period of observationbefore they can be accurately determined.This means that the certainty of the conclusions is, again, verylargely impaired: the disturbances set up as the direct effect of operation for the most part disappear as timegoes on, the explanation being that the principal path is functionally replaced by the secondary paths of whichwe spoke just now.(2) The gaps left in our knowledge by the physiological experiment are largely filled out by anatomicalinvestigation.The anatomist has followed two methods in the prosecution of his task: first, the macroscopicdissection of the hardened organ, and, later, its microscopic reduction to a series of thin sections.Of lateyears, the former of these two methods has fallen into disrepute, on the score that it runs the risk ofsubstituting artificial products of the dissecting scalpel for real fibre-tracts.Carefully applied, however, it is avaluable means of orientation with regard to certain of the wider roads of brain-travel; while its critics areinclined, on their side, to underestimate the danger of error in the interpretation of microscopic appearances.And this danger is the more serious, the farther we are from the actual attainment of the ideal goal of amicroscopic examination of the central organ, its complete reduction to an infinite series of sections ofaccurately known direction.For the rest, microscopical anatomy has been brought in recent times to a highdegree of perfection by the application of the various methods of staining [ Pobierz całość w formacie PDF ]