medical essays-第47节
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I will only call your attention to the fact； that the exceptional phenomenon of the laboratory is the prevailing law of the organism。 Nutrition itself is but one great catalytic process。 As the blood travels its rounds； each part selects its appropriate element and transforms it to its own likeness。 Whether the appropriating agent be cell or nucleus； or a structureless solid like the intercellular substance of cartilage； the fact of its presence determines the separation of its proper constituents from the circulating fluid； so that even when we are wounded bone is replaced by bone； skin by skin； and nerve by nerve。
It is hardly without a smile that we resuscitate the old question of the vis insita of the muscular fibre； so famous in the discussions of Haller and his contemporaries。 Speaking generally； I think we may say that Haller's doctrine is the one now commonly received； namely； that the muscles contract in virtue of their own inherent endowments。 It is true that Kolliker says no perfectly decisive fact has been brought forward to prove that the striated muscles contract with。 out having been acted on by nerves。 Yet Mr。 Bowman's observations on the contraction of isolated fibres appear decisive enough （unless we consider them invalidated by Dr。 Lionel Beale's recent researches； tending to show that each elementary fibre is supplied with nerves； and as to the smooth muscular fibres； we have Virchow's statement respecting the contractility of those of the umbilical cord； where there is not a trace of any nerves。
In the investigation of the nervous system； anatomy and physiology have gone hand in hand。 It is very singular that so important； and seemingly simple； a fact as the connection of the nerve…tubes； at their origin or in their course； with the nerve…cells； should have so long remained open to doubt； as you may see that it did by referring to the very complete work of Sharpey and Quain （edition of 1849）； the histological portion of which is cordially approved by Kolliker himself。
Several most interesting points of the minute anatomy of the nervous centres have been laboriously and skilfully worked out by a recent graduate of this Medical School； in a monograph worthy to stand in line with those of Lockhart Clarke； Stilling； and Schroder van der Kolk。 I have had the privilege of examining and of showing some of you a number of Dr。 Dean's skilful preparations。 I have no space to give even an abstract of his conclusions。 I can only refer to his proof of the fact； that a single cell may send its processes into several different bundles of nerve…roots； and to his demonstration of the curved ascending and descending fibres from the posterior nerveroots； to reach what he has called the longitudinal columns of the cornea。 I must also mention Dr。 Dean's exquisite microscopic photographs from sections of the medulla oblongata； which appear to me to promise a new development； if not a new epoch； in anatomical art。
It having been settled that the nerve…tubes can very commonly be traced directly to the nerve…cells； the object of all the observers in this department of anatomy is to follow these tubes to their origin。 We have an infinite snarl of telegraph wires； and we may be reasonably sure； that； if we can follow them up； we shall find each of them ends in a battery somewhere。 One of the most interesting problems is to find the ganglionic origin of the great nerves of the medulla oblongata； and this is the end to which； by the aid of the most delicate sections； colored so as to bring out their details； mounted so as to be imperishable； magnified by the best instruments； and now self…recorded in the light of the truth…telling sunbeam； our fellow…student is making a steady progress in a labor which I think bids fair to rank with the most valuable contributions to histology that we have had from this side of the Atlantic。
It is interesting to see how old questions are incidentally settled in the course of these new investigations。 Thus； Mr。 Clarke's dissections； confirmed by preparations of Mr。 Dean's which I have myself examined； placed the fact of the decussation of the pyramids denied by Haller； by Morgagni； and even by Stillingbeyond doubt。 So the spinal canal； the existence of which； at least in the adult； has been so often disputed； appears as a coarse and unequivocal anatomical fact in many of the preparations referred to。
While these studies of the structure of the cord have been going on； the ingenious and indefatigable Brown…Sequard has been investigating the functions of its different parts with equal diligence。 The microscopic anatomists had shown that the ganglionic corpuscles of the gray matter of the cord are connected with each other by their processes； as well as with the nerve…roots。 M。 Brown…Sequard has proved by numerous experiments that the gray substance transmits sensitive impressions and muscular stimulation。 The oblique ascending and descending fibres from the posterior nerve…roots； joining the 〃longitudinal columns of the cornua；〃 account for the results of Brown…Sequard's sections of the posterior columns。 The physiological experimenter has also made it evident that the decussation of the conductors of sensitive impressions has its seat in the spinal core； and not in the encephalon； as had been supposed。 Not less remarkable than these results are the facts； which I with others of my audience have had the opportunity of observing； as shown by M。 Brown…S6quard； of the artificial production of epilepsy in animals by injuring the spinal cord； and the induction of the paroxysm by pinching a certain portion of the skin。 I would also call the student's attention to his account of the relations of the nervous centres to nutrition and secretion； the last of which relations has been made the subject of an extended essay by our fellow countryman； Dr。 H。 F。 Campbell of Georgia。
The physiology of the spinal cord seems a simple matter as you study it in Longet。 The experiments of Brown…Sequard have shown the problem to be a complex one； and raised almost as many doubts as they have solved questions； at any rate； I believe all lecturers on physiology agree that there is no part of their task they dread so much as the analysis of the evidence relating to the special offices of the different portions of the medulla spinalis。 In the brain we are sure that we do not know how to localize functions； in the spinal cord； we think we do know something； but there are so many anomalies； and seeming contradictions； and sources of fallacy； that beyond the facts of crossed paralysis of sensation； and the conducting agency of the gray substance； I am afraid we retain no cardinal principles discovered since the development of the reflex function took its place by Sir Charles Bell's great discovery。
By the manner in which I spoke of the brain； you will see that I am obliged to leave phrenology sub Jove；out in the cold；as not one of the household of science。 I am not one of its haters； on the contrary； I am grateful for the incidental good it has done。 I love to amuse myself in its plaster Golgothas； and listen to the glib professor； as he discovers by his manipulations
〃All that disgraced my betters met in me。〃
I loved of old to see square…headed； heavy…jawed Spurzheim make a brain flower out into a corolla of marrowy filaments； as Vieussens had done before him； and to hear the dry…fibred but human…hearted George Combe teach good sense under the disguise of his equivocal system。 But the pseudo…sciences； phrenology and the rest； seem to me only appeals to weak minds and the weak points of strong ones。 There is a pica or false appetite in many intelligences； they take to odd fancies in place of wholesome truth； as girls gnaw at chalk and charcoal。 Phrenology juggles with nature。 It is so adjusted as to soak up all evidence that helps it； and shed all that harms it。 It crawls forward in all weathers； like Richard Edgeworth's hygrometer。 It does not stand at the boundary of our ignorance； it seems to me； but is one of the will…o'…the…wisps of its undisputed central domain of bog and quicksand。 Yet I should not have devoted so many words to it； did I not recognize the light it has thrown on human actions by its study of congenital organic tendencies。 Its maps of the。 surface of the head are； I feel sure； founded on a delusion； but its studies of individual character are always interesting and instructive。
The 〃snapping…turtle〃 strikes after its natural fashion when it first comes out of the egg。 Children betray their tendencies in their way of dealing with the breasts that nourish them； nay； lean venture to affirm； that long before they are born they teach their mothers something of their turbulent or quiet tempers。
〃Castor gaudet equis； ovo proanatus eodem Pugnis。〃
Strike out the false pretensions of phrenology； call it anthropology； let it study man the individual in distinction from man the abstraction； the metaphysical or theological lay…figure； and it becomes 〃the proper study of mankind；〃 one of the noblest and most interesting of pursuits。
The whole physiology of the nervous system； from the simplest manifestation of its power in an insect up to the supre
