a history of science-4-第49章
按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！
ir dungeons was an augury of the liberation of psychology from the musty recesses of metaphysics。 Hitherto psychology； in so far as it existed at all； was but the subjective study of individual minds； in future it must become objective as well； taking into account also the relations which the mind bears to the body； and in particular to the brain and nervous system。
The necessity for this collocation was advocated quite as earnestly； and even more directly； by another worker of this period； whose studies were allied to those of alienists； and who； even more actively than they； focalized his attention upon the brain and its functions。 This earliest of specialists in brain studies was a German by birth but Parisian by adoption； Dr。 Franz Joseph Gall； originator of the since…notorious system of phrenology。 The merited disrepute into which this system has fallen through the exposition of peripatetic charlatans should not make us forget that Dr。 Gall himself was apparently a highly educated physician； a careful student of the brain and mind according to the best light of his time； and； withal； an earnest and honest believer in the validity of the system he had originated。 The system itself； taken as a whole； was hopelessly faulty； yet it was not without its latent germ of truth； as later studies were to show。 How firmly its author himself believed in it is evidenced by the paper which he contributed to the French Academy of Sciences in 1808。 The paper itself was referred to a committee of which Pinel and Cuvier were members。 The verdict of this committee was adverse； and justly so； yet the system condemned had at least one merit which its detractors failed to realize。 It popularized the conception that the brain is the organ of mind。 Moreover； by its insistence it rallied about it a band of scientific supporters； chief of whom was Dr。 Kaspar Spurzlieim； a man of no mean abilities； who became the propagandist of phrenology in England and in America。 Of course such advocacy and popularity stimulated opposition as well； and out of the disputations thus arising there grew presently a general interest in the brain as the organ of mind； quite aside from any preconceptions whatever as to the doctrines of Gall and Spurzheim。
Prominent among the unprejudiced class of workers who now appeared was the brilliant young Frenchman Louis Antoine Desmoulins； who studied first under the tutorage of the famous Magendie； and published jointly with him a classical work on the nervous system of vertebrates in 1825。 Desmoulins made at least one discovery of epochal importance。 He observed that the brains of persons dying in old age were lighter than the average and gave visible evidence of atrophy； and he reasoned that such decay is a normal accompaniment of senility。 No one nowadays would question the accuracy of this observation； but the scientific world was not quite ready for it in 1825； for when Desmoulins announced his discovery to the French Academy； that august and somewhat patriarchal body was moved to quite unscientific wrath； and forbade the young iconoclast the privilege of further hearings。 From which it is evident that the partially liberated spirit of the new psychology had by no means freed itself altogether； at the close of the first quarter of the nineteenth century； from the metaphysical cobwebs of its long incarceration。
FUNCTIONS OF THE NERVES
While studies of the brain were thus being inaugurated； the nervous system； which is the channel of communication between the brain and the outside world； was being interrogated with even more tangible results。 The inaugural discovery was made in 1811 by Dr。 （afterwards Sir Charles） Bell；＇1＇ the famous English surgeon and experimental physiologist。 It consisted of the observation that the anterior roots of the spinal nerves are given over to the function of conveying motor impulses from the brain outward； whereas the posterior roots convey solely sensory impulses to the brain from without。 Hitherto it had been supposed that all nerves have a similar function； and the peculiar distribution of the spinal nerves had been an unsolved puzzle。
Bell's discovery was epochal； but its full significance was not appreciated for a decade； nor； indeed； was its validity at first admitted。 In Paris； in particular； then the court of final appeal in all matters scientific； the alleged discovery was looked at askance； or quite ignored。 But in 1823 the subject was taken up by the recognized leader of French physiologyFrancois Magendiein the course of his comprehensive experimental studies of the nervous system； and Bell's conclusions were subjected to the most rigid experimental tests and found altogether valid。 Bell himself； meanwhile； had turned his attention to the cranial nerves； and had proved that these also are divisible into two setssensory and motor。 Sometimes； indeed； the two sets of filaments are combined into one nerve cord； but if traced to their origin these are found to arise from different brain centres。 Thus it was clear that a hitherto unrecognized duality of function pertains to the entire extra…cranial nervous system。 Any impulse sent from the periphery to the brain must be conveyed along a perfectly definite channel； the response from the brain； sent out to the peripheral muscles； must traverse an equally definite and altogether different course。 If either channel is interruptedas by the section of its particular nerve tractthe corresponding message is denied transmission as effectually as an electric current is stopped by the section of the transmitting wire。
Experimenters everywhere soon confirmed the observations of Bell and Magendie； and； as always happens after a great discovery； a fresh impulse was given to investigations in allied fields。 Nevertheless； a full decade elapsed before another discovery of comparable importance was made。 Then Marshall Hall； the most famous of English physicians of his day； made his classical observations on the phenomena that henceforth were to be known as reflex action。 In 1832； while experimenting one day with a decapitated newt； he observed that the headless creature's limbs would contract in direct response to certain stimuli。 Such a response could no longer be secured if the spinal nerves supplying a part were severed。 Hence it was clear that responsive centres exist in the spinal cord capable of receiving a sensory message and of transmitting a motor impulse in replya function hitherto supposed to be reserved for the brain。 Further studies went to show that such phenomena of reflex action on the part of centres lying outside the range of consciousness； both in the spinal cord and in the brain itself； are extremely common； that； in short； they enter constantly into the activities of every living organism and have a most important share in the sum total of vital movements。 Hence； Hall's discovery must always stand as one of the great mile…stones of the advance of neurological science。
Hall gave an admirably clear and interesting account of his experiments and conclusions in a paper before the Royal Society； 〃On the Reflex Functions of the Medulla Oblongata and the Medulla Spinalis；〃 from which； as published in the Transactions of the society for 1833； we may quote at some length：
〃In the entire animal； sensation and voluntary motion； functions of the cerebrum； combine with the functions of the medulla oblongata and medulla spinalis； and may therefore render it difficult or impossible to determine those which are peculiar to each； if； in an animal deprived of the brain； the spinal marrow or the nerves supplying the muscles be stimulated； those muscles； whether voluntary or respiratory； are equally thrown into contraction； and； it may be added； equally in the complete and in the mutilated animal； and； in the case of the nerves； equally in limbs connected with and detached from the spinal marrow。
〃The operation of all these various causes may be designated centric； as taking place AT； or at least in a direction FROM； central parts of the nervous system。 But there is another function the phenomena of which are of a totally different order and obey totally different laws； being excited by causes in a situation which is EXCEN
