

May 3, 1888] 



NA TURE 



19 



a great height above their bases. The group is situated on the 

 north easterly projection of the axis of the volcanic zone of the 

 Bay of Plenty, which, continued still further north- eastward, 

 strikes the Tonga and Samoan Croups, places where volcanic 

 action is still going on. Two, if not three, volcanic disturb- 

 ances have taken place at the Kermadec Islands within recent 

 years, and earthquakes were very frequent there at one time ; 

 but since the eruption of Tarawera, June io, 1886, they have 

 ceased entirely. On Sunday Island the mo^t prominent feature 

 is the large crater near the centre of the island. It is I \ mile 

 long by i:i ni 'le wide; its walls are generally over 1000 feet 

 high. Steam escapes occasionally from the (ireen Lake on the 

 south side, and from the crevices in the precipitous cliffs of 

 Denham Bay, while warm water oozes out of the sand on the 

 north coa-t. 



Dr. Hans Meyer, who recently ascended Kilimanjaro, and 

 Dr. O. Haumann, who accompanied Dr. Lenz up the Congo, 

 are preparing to start on a new expedition to East Africa. Their 

 object will be to make a thorough exploration and survey of the 

 whole of the Kilimanjaro region. 



Recent issues of the journals published in French Indo-China, 

 contain an interesting letter from M. Gauthier, describing a 

 journey down the Meikong River, from Luang Prabang* into 

 Cambodia. The traveller spent forty days on the journey, and 

 passed twenty cataracts, in one of which his boat was almost 

 dashed to pieces. He visited the Laos States, and describes its 

 inhabitants as doing nothing except laughing, smoking, and 

 singing throughout the day, such business as there is being wholly 

 in the hands of the Chinese. 



OUR ELECTRICAL COLUMN. 



Gouy has found that the attraction between two electrified 

 surfaces maintained at a constant potential-difference is one 

 hundred times greater in distilled water than in air. 



Admirably well-equipped public electrical laboratories have 

 been established in Paris and Vienna. When are we to see one 

 in London ? 



Van Aubet. {Arch, de Geneve, xix. p. 105, 1888) has been 

 studying the effect of magnetism and heat on the electric resist- 

 ance of bismuth and of its alloys with lead and tin. Contrary 

 to all other metals, the resistance of bismuth sometimes increases 

 with reduction of temperature. He also verified the fact that 

 the resistance of bismuth at low temperatures increases in the 

 magnetic field. The effect is very feeble with alloys. 



Foeppi. {Ann. Wiedemann, xxxiii. p. 492) has been endea- 

 vouring to prove Edlund's hypothesis that a perfect vacuum is 

 a conductor, but has completely failed to do so. He makes the 

 resistance of a vacuum to be three million times greater than 

 that of copper. 



Mr. C. Vernon Koys has communicated to the Royal 

 Society some further details of his beautiful radio-micrometer. 

 It is a thermo-electric circuit, consisting of a bar of antimony 

 and bismuth, of small sectional area, the ends being formed by 

 a loop of copper wire, suspended by a torsion fibre in a strong 

 magnetic field. It is possible to observe by its means a difference 

 of temperature of one ten-millionth of a degree Centigrade. 



C. L. Weber {Centralbla't fur Elek'rotechnik, 1887, vol. ix.), 

 experimenting on various amalgams and alloys of tin, bismuth, 

 lead, and cadmium, has found that many of them have a higher 

 conductivity than that of each of their constituents. 



Sirks, of Deventer (Holland), has found a peculiar dynamical 

 action of the current on the electrodes. An electrical current 

 passing through a solution of C11SO4 between two electrodes of 

 copper, which are varnished at the back, pulls both against the 

 direction of the positive stream. Independently of the con- 

 centration, if only high enough to prevent the formation of 

 gases, the pressure at the anode and the traction at the kathode 

 amount to nearly 1 gramme per ampere and per square metre. 



ON THE COMPARISON OF THE CRANIAL 

 WITH THE SPINAL NERVES. 



'"THE origin of vertebrate animals is to be found according to 

 many morphologists in those invertebrates which are com- 

 posed of a series of segments, and one of the chief arguments in 

 favour of this view has always been the fact that the spinal 



nerves are arranged segmentally. It has, however, long been 

 felt that the cranial nerves ought to give evidence of a segmental 

 arrangement as clearly as the spinal before it is possible to 

 speak of a segmentation based upon the arrangement of the 

 nervous system ; and indeed many ingenious tables have been 

 manufactured by morphologists in order to bring the cranial 

 nerves into the same system as the spinal. The failure of these 

 attempts is to my mind due largely to the following reasons : — 



1. Confusion has arisen because anatomists have been in the 

 habit of looking upon the nervous system of the vertebrate as 

 composed of two separate nervous systems, viz. the cerebro- 

 spinal and sympathetic. 



2. In the comparison of cranial and spinal nerves the morpho- 

 logists have directed their attention too exclusively to the exits 

 of the nerves from the central nervous system without taking 

 into account the place of origin of the nerves in the central 

 nervous system itself. 



3. It has been assumed on insufficient grounds that the 

 presence of ganglia in connection with motor cranial nerves 

 indicates that the cranial nerves do not follow Bell's law, 

 and are therefore not strictly comparable with spinal nerves. 



These difficulties are all found to vanish as soon as a clear 

 conception is obtained of what is meant by the nerves of a 

 spinal segment. 



Since the time of Charles Bell it has been recognized that a 

 spinal nerve is formed by two roots : the one, posterior, which 

 contains only afferent fibres, i.e. fibres which convey impulses 

 from the periphery to the central nervous system ; and the other, 

 anterior, containing exclusively efferent fibres which convey 

 impulses from the central nervous system to the periphery. In 

 correspondence with these two sets of fibres the grey matter of 

 the spinal cord is divided into two portions, named respectively 

 ths posterior and anterior horns. Another division, however, 

 exists of almost equal importance, which is not so generally 

 recognized, viz. a division both of the nerve fibres and their 

 centres of origin in the grey matter for the purpose of supplying 

 the internrd and external portions of the body — a division of 

 nerves and nerve centres into splanchnic and somatic as well 

 as into afferent and efferent. The centres of origin of the 

 splanchnic nerves are situated in the internal part of the grey 

 matter of the spinal cord, being arranged in groups in the 

 neighbourhood of the central canal, and the nerves themselves 

 supply the viscera and internal surfaces of the body, together 

 with certain muscles of respiration and deglutition which are 

 derived from special embryonic structures known as the lateral 

 plates of mesoblast. On the other hand, the centres of origin 

 of the somatic nerves are situated in the outlying horns of grey 

 matter, and the nerves themselves supply the integument and 

 the ordinary muscles of locomotion, &c., — muscles which are 

 derived from the muscle-plates or myotomes. 



Further, these two sets of nerves are arranged in the posterior 

 and anterior roots in a special manner, the significance of which 

 is the key to the whole question of the segmental nature of the. 

 cranial nerves. In the posterior roots the afferent fibres of both 

 splanchnic and somatic systems pass into the spinal ganglion, 

 which is always situated on the nerve root soon after its exit 

 from the central nervous system ; so that we may speak of the 

 afferent fibres of both systems as being in connection with a 

 ganglion which is stationary in position. In the anterior roots, 

 on the other hand, we find that some of the fibres are in con- 

 nection with no ganglia, while others are in connection with 

 ganglia which are not fixed in position, but are found at various 

 distances from the central nervous system (it is this system of 

 ganglia which has hitherto been looked upon as forming a 

 separate nervous system, viz. the sympathetic system), so that 

 the fibres of the anterior root, all of which are efferent, are 

 divisible into a ganglionattd and a non-ganglionated group, of 

 which the ganglionated group belongs to the splanchnic system, 

 and is characterized by the smallness in the size of its fibres, 

 while the non-ganglionated group is composed both of somatic 

 and splanchnic nerves, and forms the ordinary large-sized mctor 

 nerve fibres of the voluntary striped muscles both of respiration 

 and deglutition as well as of locomotion. 



Again, it has been shown that these efferent ganglia are in 

 reality offshoots from a primitive ganglion mass situated on the 

 spinal nerves into which both afferent and efferent fibres ran. 



We see, then, that both roots of a fully formed spinal nerve are 

 ganglionated, so that the presence of a ganglion is no longer the 

 sign of a posterior root, and we must define a spinal nerve as 

 being formed by — 



