a history of science-4-第56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！
ities unquestionably depend in part upon the supply of arterial blood； this peculiar arrangement of the vascular mechanism may very properly be supposed to aid in the localized activities of the central nervous ganglia。 But this explanation left much to be desiredin particular when it is recalled that all higher intellection must in all probability involve multitudes of widely scattered centres。
No better explanation was forthcoming； however； until the year 1889； when of a sudden the mystery was cleared away by a fresh discovery。 Not long before this the Italian histologist Dr。 Camille Golgi had discovered a method of impregnating hardened brain tissues with a solution of nitrate of silver； with the result of staining the nerve cells and their processes almost infinitely better than was possible by the methods of Gerlach； or by any of the multiform methods that other workers had introduced。 Now for the first time it became possible to trace the cellular prolongations definitely to their termini； for the finer fibrils had not been rendered visible by any previous method of treatment。 Golgi himself proved that the set of fibrils known as protoplasmic prolongations terminate by free extremities； and have no direct connection with any cell save the one from which they spring。 He showed also that the axis cylinders give off multitudes of lateral branches not hitherto suspected。 But here he paused； missing the real import of the discovery of which he was hard on the track。 It remained for the Spanish histologist Dr。 S。 Ramon y Cajal to follow up the investigation by means of an improved application of Golgi's method of staining； and to demonstrate that the axis cylinders； together with all their collateral branches； though sometimes extending to a great distance； yet finally terminate； like the other cell prolongations； in arborescent fibrils having free extremities。 In a word； it was shown that each central nerve cell； with its fibrillar offshoots； is an isolated entity。 Instead of being in physical connection with a multitude of other nerve cells； it has no direct physical connection with any other nerve cell whatever。
When Dr。 Cajal announced his discovery； in 1889； his revolutionary claims not unnaturally amazed the mass of histologists。 There were some few of them； however； who were not quite unprepared for the revelation； in particular His； who had half suspected the independence of the cells； because they seemed to develop from dissociated centres； and Forel； who based a similar suspicion on the fact that he had never been able actually to trace a fibre from one cell to another。 These observers then came readily to repeat Cajal's experiments。 So also did the veteran histologist Kolliker； and soon afterwards all the leaders everywhere。 The result was a practically unanimous confirmation of the Spanish histologist's claims； and within a few months after his announcements the old theory of union of nerve cells into an endless mesh…work was completely discarded； and the theory of isolated nerve elementsthe theory of neurons； as it came to be calledwas fully established in its place。
As to how these isolated nerve cells functionate； Dr。 Cajal gave the clew from the very first； and his explanation has met with universal approval。
In the modified view； the nerve cell retains its old position as the storehouse of nervous energy。 Each of the filaments jutting out from the cell is held； as before； to be indeed a transmitter of impulses； but a transmitter that operates intermittently； like a telephone wire that is not always 〃connected；〃 and； like that wire； the nerve fibril operates by contact and not by continuity。 Under proper stimulation the ends of the fibrils reach out； come in contact with other end fibrils of other cells； and conduct their destined impulse。 Again they retract； and communication ceases for the time between those particular cells。 Meantime； by a different arrangement of the various conductors； different sets of cells are placed in communication； different associations of nervous impulses induced； different trains of thought engendered。 Each fibril when retracted becomes a non…conductor； but when extended and in contact with another fibril； or with the body of another cell； it conducts its message as readily as a continuous filament could doprecisely as in the case of an electric wire。
This conception； founded on a most tangible anatomical basis； enables us to answer the question as to how ideas are isolated； and also； as Dr。 Cajal points out； throws new light on many other mental processes。 One can imagine； for example； by keeping in mind the flexible nerve prolongations； how new trains of thought may be engendered through novel associations of cells； how facility of thought or of action in certain directions is acquired through the habitual making of certain nerve…cell connections； how certain bits of knowledge may escape our memory and refuse to be found for a time because of a temporary incapacity of the nerve cells to make the proper connections； and so on indefinitely。
If one likens each nerve cell to a central telephone office； each of its filamentous prolongations to a telephone wire； one can imagine a striking analogy between the modus operandi of nervous processes and of the telephone system。 The utility of new connections at the central office； the uselessness of the mechanism when the connections cannot be made； the 〃wires in use〃 that retard your message； perhaps even the crossing of wires； bringing you a jangle of sounds far different from what you desireall these and a multiplicity of other things that will suggest themselves to every user of the telephone may be imagined as being almost ludicrously paralleled in the operations of the nervous mechanism。 And that parallel； startling as it may seem； is not a mere futile imagining。 It is sustained and rendered plausible by a sound substratum of knowledge of the anatomical conditions under which the central nervous mechanism exists； and in default of which； as pathology demonstrates with no less certitude； its functionings are futile to produce the normal manifestations of higher intellection。
X。 THE NEW SCIENCE OF ORIENTAL ARCHAEOLOGY
HOW THE 〃RIDDLE OF THE SPHINX〃 WAS READ
Conspicuously placed in the great hall of Egyptian antiquities in the British Museum is a wonderful piece of sculpture known as the Rosetta Stone。 I doubt if any other piece in the entire exhibit attracts so much attention from the casual visitor as this slab of black basalt on its telescope…like pedestal。 The hall itself； despite its profusion of strangely sculptured treasures； is never crowded； but before this stone you may almost always find some one standing； gazing with more or less of discernment at the strange characters that are graven neatly across its upturned； glass…protected face。 A glance at this graven surface suffices to show that three sets of inscriptions are recorded there。 The upper one； occupying about one…fourth of the surface； is a pictured scroll； made up of chains of those strange outlines of serpents； hawks； lions； and so on； which are recognized； even by the least initiated； as hieroglyphics。 The middle inscription； made up of lines； angles； and half…pictures； one might surmise to be a sort of abbreviated or short…hand hieroglyphic。 The third or lower inscription is Greekobviously a thing of words。 If the screeds above be also made of words； only the elect have any way of proving the fact。
Fortunately； however； even the least scholarly observer is left in no doubt as to the real import of the thing he sees； for an obliging English label tells us that these three inscriptions are renderings of the same message； and that this message is a 〃decree of the priests of Memphis conferring divine honors on Ptolemy V。 （Epiphenes）； King of Egypt； B。C。 195。〃 The label goes on to state that the upper inscription （of which； unfortunately； only part of the last dozen lines or so remains； the slab being broken） is in 〃the Egyptian language； in hieroglyphics； or writing of the priests〃； the second inscription 〃in the same language is in Demotic； or the writing of the people〃； and the third 〃the Greek language and character。〃 Following
