Dec. 23, 1886] 



NA TURE 



185 



each end of the calc crystal so as to make the new end-faces 

 almost co-planar with a principal plane of section, and the 

 crystal is cut through along the other diagonal of the sides. 

 The results may be tabulated thus : — 



Ordinary Nicol 



69 



Obliquity of end-face ... ... 71 



Angle between end-face and crys- 



tallographic axis ... ... 45 ... 5 



Angle between balsam-film and 



crystallographic axis ... ... 45 ... 94 



The effect is to throw the blue-iris limit right back, to shorten 

 the prism, and to widen the field. In the discussion that fol- 

 lowed, Prof. Stokes remarked that there was no dearth of Ice- 

 land spar in Iceland, but that the supply bad been limited 

 through ignorance of the extent of the demand. The mine 

 had, however, been bought by the Icelandic Government, and 

 a plentiful supplylmight therefore be expected. 



THE SYMPATHETIC NERVOUS SYSTEM^ 

 T^HE lecturer commenced by giving a short sketch of Bichat's 

 views of the division of life into organic and animal life, 

 and pointed out how that division naturally led to the concep- 

 tion of two separate central nervous systems, the one, the 

 sympathetic, to which all the organic functions are to be re- 

 ferred, the other, the cerebro-spinal, regulating the animal 

 functions. He then pointed out how Remak's discovery of a 

 special kind of nerve-fibre — the non-medullated nerves — asso- 

 ciated only with the ganglia of the sympathetic system, tended 

 strongly to confirm Bicbat's teaching of the existence of two 

 separate central nervous .systems in the human body, each of 

 which communicated with the other by means of its own special 

 kind of nerve-fibres ; the cerebro-spinal supplying the sympa- 

 thetic system with white medullaled fibres, and the sympathetic 

 supplying the cerebro-spinal with gray or gelatinous non-medul- 

 lated fibres. He then continued as follows : — 



Even at the present day the teaching of Bichat still very 

 largely holds its ground. It is true that the tendency of modern 

 physiology is to increase the number of centres of action for the 

 organic ner\'es, which exist in the cerebro-spinal central axis, 

 and therefore to do away with the necessity for a separate inde- 

 pendent sympathetic nervous system, yet the automatic actions 

 of isolated organs such as the heart, and the existence of special 

 nerve-fibres in connection with this system, still induce the 

 neurologists of the present day to place the sympathetic 

 nervous sy.^tem on an equality with the brain or spinal 

 cord. In this lecture to-night I hope to give the death-blow to 

 Bichat's teaching, and to prove to you that the whole sympa- 

 thetic system is nothing more than an outflow of visceral nerves 

 from certain nerve-centres in the cerebro-spinal system, the 

 ganglia of which are not confined to one fixed position, as is the 

 ca-se with the ganglia of the posterior roots, but have travelled 

 further away from the central axis. 



I do not propose to night to deal with the argument for the 

 independence of the sympathetic nervous system, which is based 

 upon the automatism of such isolated organs as the heart ; I 

 have already in various papers given the reasons and arguments 

 why I look upon such automatic movements as due to the 

 automatism of the cardiac muscular tis.^ue rather than to any 

 action of nerve-cells comparable to the nerve-centres of the 

 spinal cord ; I shall deal entirely with the anatomical argument, 

 and show you step by step how the nerve-fibres which constitute 

 the sympathetic system can be traced to their origin in the central 

 cerebro spinal axis. 



Evidently, in endeavouring to determine by anatomical means 

 \\ hether the sympathetic and cerebro-spinal systems are in reality 

 independent of one another, our attention must necessarily be 

 especially concentrated upon the nature of the connecting-link be- 

 tween the two systems, i.e. upon the nature of the rami communi- 

 cantes. Largely owing to the pre-conceived notions of anatom- 

 ists, you will find that the rami communicantes are arranged 

 symmetrically in connection w ith all the spinal nerves of the 

 body. In reality this is far from being the case ; the rami com- 

 municantes of the thoracic nerves differ from those above them, 

 i.e. of the cervical nerves, and from those below them, 



* Abstract of Lecture at the Roy.al Institution 

 Walter H. Gaskell, M.D., M.A., F.R.S. 



Jun 



iS36, by 



i.e. of the lumbar nerves, in two important particulars : in the 

 first place the corresponding sympathetic ganglion is connected 

 with each thoracic nerve by two rami communicantes ; and 

 secondly, these two rami differ in colour, one being gray, i.e. 

 composed almost entirely of non-medullated nerves, and the 

 other white, i.e. composed essentially of medullated nerve- 

 fibres. ' 



Tills double nature of the ramus communicans is confiiied 

 to the region lying between the two large plexuses which 

 suiply the anterior -and posterior extremities, viz. the brachial, 

 lumbar, and sciatic plexuses ; the rami communicantes to the 

 lower cervical and first thoracic nerves, as well as those to the 

 nerves forming the anterior crural and the sciatic, are, on the 

 other hand, single, and are composed only of gray rami. In 

 other v\ ords, the sympathetic chain is connected with the central 

 nervous system by means of white rami communicantes only 

 between the second thoracic and second lumbar nerves. 



hurther, I have been able to trace both the white and gray 

 rami in their journey to the spinal cord by means of consecutive 

 sections of osmic acid preparations, and have found that the gray 

 rami pass out of the sympathetic ganglion as a single nerve, and 

 then ramify in the connective tissue about the vertebral fora- 

 mina, a portion only reaching the spinal nerve-trunk ; the gray 

 fibres of this portion pass mainly along the nerve peripherally, 

 the few which pass centrally never reach the spinal cord, but 

 pass out with the connective tissue which lies in between the 

 medullated nerve-fibres of the anterior and posterior roots, to 

 ramify over and to supply the blood-vessels of the various mem- 

 branes which inclose the spinal cord. 



In fact the gray rami communicantes are peripheral nerves, 

 which partly supply the vertebr.Te and the membranes of the cord, 

 and partly pass to their destination in the same direction as the 

 eff'erent fibres of the spinal nerve itself. 



So far then I come to these conclusions : — 



(1) The sympathetic does not send non-medullated fibres into 

 the cerebro-spinal system, because these fibres all pass out of the 

 nerve-roots before they reach the spinal cord. 



(2) White or medullated nerve-fibres constitute the only link 

 between the sympathetic and cerebro-spinal systems, constituting 

 the white rami communicantes. 



(3) Consequently the connection between these two nervous 

 systems is limited to the region of white rami communicantes, 

 i.e. to the region between the second thoracic and second lumbar 

 nerves. 



Further, these conclusions are borne out when we attempt to 

 follow the white rami commnnicantes into the central spinal 

 axis by means of their structural peculiarities ; sections of osmic 

 preparations show that each white ramus is composed chiefly of 

 very small medullated nerve-fibres, varying in size from i '8 /i to 

 36 fj., very much smaller, therefore, than the large medullated 

 nerves which form the bulk of the anterior roots of the spinal 

 nerves, these latter varying between 14 /i to 20 fi or even larger. 

 Clearly then the fibres of the white ramus communicans ought 

 to show very conspicuously among the large fibres of the anterior 

 roots whenever they are present in those roots. I have cut sec- 

 tions of the anterior roots of all the spinal nerves in the dog; 

 and have found, as I show you on this screen, that these very 

 fine medullated nerve-fibres make their appearance for the first 

 time in the anterior roots of the second thoracic nerve ; they are 

 found in large quantities in all the anterior roots between the 

 second thoracic and second lumbar, and then again the anterior 

 roots immediately below the second lumbar are free from such 

 groups of very fine fibres. We see then that exactly corre- 

 sponding to the presence of white rami communicantes in the 

 thoracic region we find groups of characteristic fine medullated 

 fibres existing in the anterior roots, fibres which cleariy form 

 part of the white ramus communicans, and confirm by their 

 presence the conclusion already arrived at, viz. that the nerves 

 which pass from the spinal cord into the sympathetic system are 

 limited to the thoracic region of the cord. 



We can no^v go a step further and argue in the reverse direc- 

 tion that the presence of groups of these very fine medullated 

 fibres in the anterior roots of any nerve implies the existence of 

 nerve- fibres belonging to the same system as the white rami 

 communicantes or rami viscerales, as we may now call them. 

 Examination shows how just is this argument, for I find that 

 the same groups of fine nerve-fibres suddenly appear again in 

 the anterior roots of the second and third sacral nerves, and can 

 be traced into that well-known nerve which passes from the 

 second and third sacral nerves into the hypogastric plexus to 



