sations; that the stomato-gastric, respiratory, and locomotive centres are all united in the spinal cord of the vertebrata, where they form one continuous ganglionic mass, and that the nerves connected with all these likewise receive fibres derived immediately from the cephalic ganglia;and lastly, that whenever peculiar consentaneousness of action is required between different organs, their ganglionic centres are united more or less closely; and that the trunks themselves are generally connected by bands of communication.

On the whole, in the present state of our knowledge, we are justified, perhaps, in adopting the systematic summary of the functions of the nervous system, and the general purposes to which it is inservient, as given by the writer last cited. 1. The nervous system receives impressions, which, being conveyed by its afferent fibres to the sensorium, are there communicated to the conscious mind; and are inservient, in some manner, to the acts of that mind. As the result of these acts, a motor impulse is transmitted along efferent nerves to particular muscles, which excites them to contraction. Of these acts the encephalon, and nerves communicating with it, are the organs. 2. Certain parts of the nervous system receive impressions, which are propagated along afferent fibres that terminate in ganglionic centres distinct from the sensorium. In these, a reflex motor impulse is thus excited, which is transmitted along efferent trunks proceeding from those centres, and excites muscular contraction without any necessary intervention of sensation or volition. The organs of this function are the gray matter of the spinal cord, which is not continuous with the fibrous structure of the brain, and the trunks connected with it. It is the true spinal or excito-motory system of Dr. Hall. 3. There is yet a division of the nervous system, which appears to have for its object to combine and harmonize the muscular movements immediately connected with the maintenance of organic life. It may likewise influence, and connect with each other the functions of nutrition, secretion, &c.; although these-like the muscular movements immediately connected with the maintenance of organic life-are doubtless essentially independent of it; and—as has been shown-can be carried on where it does not exist. The organ of these acts is the great sympathetic. Of late-as will be seen hereafter-Dr. Carpenter has contended with much force for the existence of a series of sensory ganglia, separate and distinct from those that compose the cerebrum and cerebellum-" ganglia of the nerves of sensation, common and special, which are superposed, as it were, on the medulla oblongata," and which, together, constitute the real sensorium.

It has been urged by Dr. Laycock,3 in a paper read before the British Association at York, in accordance with views published by him four years previously, that the brain, although the organ of consciousness, is subject also to the laws of reflex action; and that in this respect it does not differ from other ganglia of the nervous system. He

'Human Physiology, p. 79, London, 1842.

'Principles of Human Physiology, 4th Amer. edit., p. 320, Philad., 1850.
3 British and Foreign Medical Review, Jan., 1845, p. 298.

regards the cerebral nerves, and especially the optic, auditory, and olfactory, as afferent excitor nerves, along which impressions pass to the central axis; thence to, be communicated to the motor nerves, and thus give rise to combined muscular acts, or to irregular spasmodic movements. Hydrophobia is adduced by him as a good illustration of these cerebral reflex movements. The acknowledged excito-motory phenomena in the disease may be induced.-First. Through the nerves of touch, as by the contact of water with the surface of the head, hands, chest, lips, and pharynx. Secondly. By a current of air impinging on the face or chest. Thirdly. By a bright surface, as a mirror. Fourthly. By the sight of water; and Fifthly. By the idea of water, as when it is suggested to the patient to drink.

The author has been in the habit of offering as an example of the same kind, vomiting induced by the sight of a disgusting object. Here the impression is first made upon the brain through an organ of sense, and the reflex motor phenomena concerned in vomiting are instantaneously excited;-facts, which at least prove, that although the gray matter of the spinal marrow may continue to execute its functions, when those of the cerebro-spinal nervous system are suspended, -as during sleep or an attack of epilepsy, it is capable of being excited to action by impressions made through the latter, in the same manner as by impressions made on the afferent spinal nerves themselves.

Fig. 24.

A

From all that has been said, it will be understood, that each nerve as it issues from the spinal canal must be composed of various fasciculi:-one, sensory or of sensation, connected with the posterior medullary tract, and continuous with the medullary matter of the brain; another, connected with the anterior medullary tract, and conveying the influence of volition from the brain along the spinal cord and nerves to the muscles; a third, consisting of excitor fibres, terminating in the gray or ganglionic matter of the cord, and conveying impressions to it; and a B fourth, consisting of motor fibres, arising from the gray matter of the cord, and conveying the nervous influence reflected to the muscles.

with the anterior of the same side,

It would appear that a part of each root enters the gray matter of the cord; whilst a part is continuous with the white or medullary matter; and Dr. Stilling' affirms-as the reSult of his researches-that of the fibres of the posterior roots some form loops in the gray matter, and become continuous with those of the anterior roots of the same side; whilst others cross the

A. Posterior fibres continuous through the nucleus of the cord. B. Posterior fibres continuous with

the anterior of the opposite side.

1 Untersuchungen über die Textur des Rückenmarks, von Dr. B. Stilling und Dr. J. Wallch, s. 51. Leipz., 1842.

Fig. 25.

gray matter, and become continuous with those of the anterior roots of the opposite side. It has been shown, too, by Mr. Newport,' that there are other fibres, which pass from the posterior into the anterior roots of other nerves, above and below, both on the same and the opposite of the nerves; the longitudinal white and gray fibres are inside.

Transverse Section of the Medulla. (After Stilling.)

The transverse gray fibres are the continuation of the roots dicated by points.

Much, doubtless, still remains to be accomplished, before we can consider views in regard to the nervous system established. Like many important questions of physiology, they may be regarded as in a transition state; but the zeal and activity of physiological inquirers are daily throwing light upon many points; and of these there are none surrounded with more obscurity than those that appertain to the nervous system.

All the parts described as constituting the nervous system-brain, cerebellum, medulla spinalis, and nerves-are formed of the primary nervous fibre, the nature of which has been already described. The neurine or substance of which they are constituted is soft and pulpy; but the consistence varies in different portions, and, in the whole, at different ages. In the fœtus it is almost fluid; in youth of greater firmness; and in the adult still more so. This softness of structure in the encephalon of the foetus is by no means inutile. It admits of the pressure, which takes place, to a greater or less extent in all cases of parturition, whilst the head is passing through the pelvis, without the child sustaining any injury. On examining, however, the consistence of dif ferent brains, it is necessary to inquire into the period that has elapsed since the death of the individual, as the brain loses its firmness by being kept; and ultimately becomes semifluid. It is likewise rendered fluid by disease, constituting ramollissement du cerveau or mollescence of the brain, to which the attention of pathologists has been directed of late years, but without much important advantage to science.

When the encephalon is fresh, it has a faint, spermatic, and somewhat tenacious smell. This, according to M. Chaussier, has persisted for years in brains that have been dried.

2

Neurine has been subjected to analysis by M. Vauquelin, and found to contain, water, 80.00; white fatty matter, 4.53; red fatty matter, called cerebrin, 0.70; osmazome, 1.12; albumen, 7.00; phosphorus, 1.50; sulphur, acid phosphates of potassa, lime, and magnesia, 5·15. M. Couerbe's analysis of that of the brain3 gives, 1. A pulverulent yellow fat, stearconote; 2. An elastic yellow fat, cerancephalote; 3. A reddish-yellow oil, eleancephol; 4. A white fatty matter, cerebrote,

1845.

Philosophical Transactions, 1843, and Dr. Carpenter, 2d Amer. edit., p. 125, Philad., 'Annales de Chim., lxxxi. 37; and Annals of Philosophy, i. 332. Annales de Chimie et de Physique, lvi. 160.

the white fatty matter of Vauquelin, the myelocone of Kühn; 5. Cerebral cholesterin-cholesterote; and the salts found by Vauquelin,lactic acid, sulphur, and phosphorus, which form a part of the fats above-mentioned. In the spinal cord, there is more fatty matter, and less osmazome, albumen, and water. In the nerves, albumen predominates, and fatty matters are less in quantity. Researches by M. Lassaigne show, that water constitutes ths of the nerves; and ths of 10 the brain; whilst the proportion of albumen in the former is 22ths; in the latter, ths. He found the neurine of different parts of the brain to be composed as follows:

Water,

10

8

M. Raspail3 has pointed out two other differences. First, when a nerve is left upon a plate of glass in dry air, it becomes dry, without putrefying, whilst cerebral neurine putrefies in twenty-four hours; and secondly, the dried nerve has all the physical characters of the corneous substances, nails, hair, and other analogous bodies; and in their chemical relations, these bodies do not differ sufficiently to repel the analogy. Neither the chemical analysis of neurine, nor inquiry into its minute structure by the aid of the microscope, has, however, thrown light upon the wonderful functions executed by this elevated part of the organism.

It would seem, that neurine is, in composition, intermediate between fat and the compounds of protein: it contains nitrogen, which is not present in fats, but in smaller proportion than in protein; and, on the other hand, it is much richer in carbon than protein or its compounds. Phosphorus, too, is an essential ingredient. According to recent researches by M. Frémy, there is in cerebral neurine a peculiar acid, analogous to the fatty acids, which he calls cerebric acid, and which contains nitrogen and phosphorus: this is mixed with an albuminous substance; with an oily acid-oleo-phosphoric; with cholesterin; and with small quantities of olein and margarin, and oleic and margaric acids.

To the naked eye, neurine appears under two forms;-the one gray and of a softer consistence; the other white, and more compact. The former is called the vesicular, gray, cortical, cineritious, or pulpy substance; the latter, the tubular, white, medullary, or fibrous, called "tubular" in consequence of its consisting of tubes of great minuteness, which are filled with a kind of granular pith that can be squeezed from them, a view adopted by most histologists. Dr. James Stark has,5

'For John's Analysis of the white and gray cerebral matter, see Journal de Chimie Médicale, Août, 1835. See, also, Simon's Medical Chemistry, p. 81, Lond., 1845.

Journal de Chim. Médic.; and Pharmaceutisches Central Blatt, Nov. 19, 1836, s. 765. 3 Chimie Organique, p. 217, Paris, 1833.

4 Journ. des Connais. Méd.-Chir., Jan., 1841; also Turner and Liebig's Chemistry, 7th edit., p. 1195, Lond., 1842.

• Proceedings of the Royal Society, No. 56, Lond., 1843.

however, affirmed, as the result of his examination, that the matter which fills the tubes is of an oily nature, differing, in no essential respect, from butter or soft fat, and remaining of a fluid consistence during the life of the

animal, or whilst it retains its natural temperature; but becoming granular or solid when the animal dies. The diameter of these cylindrical tubuli has been estimated to vary from about the 6th to the ath of a line. The nerves are wholly composed of it.

Tubular Nerve-fibres.

1

The tubular nervous
matter, wherever it is
found, seems to consist
of fibres, which have a
definite arrangement.
Two kinds of primitive
fibre, according to the
researches of Messrs.
Todd and Bowman,1 are
present in the nervous
system, which they dis-
tinguish as the tubular
fibre or nerve tube, and
the gelatinous fibre,-
the former infinitely the
more numerous, and the
latter found chiefly in
the sympathetic system. The tubular
fibres vary in diameter from th even
to both of an inch; but their average
width is from oth tooth of an inch.
The gelatinous fibre is devoid of the
whiteness that characterizes the tubular
fibre; and the gray colour of certain
nerves, it has been thought, is dependent
chiefly upon the presence of a large
proportion of gelatinous fibres. Hence
they have been sometimes termed gray
fibres. These are in general smaller
than the tubular fibres,-their dia-
meter ranging between the sooth and Hannover; c and d after Remak.)
the 70th of an inch.

A. Tubular nerve-fibres, showing the sinuous outline and double
B. Diagram to show the parts of a tubular fibre, viz.: 1, 1. Mem-

contours.
branous tube. 2, 2. White substance or medullary sheath. 3. Axis
or primitive band.

c. Figure (imaginary) intended to represent the appearances occasionally seen in the tubular fibres. 1, 1. Membrane of the tube seen at parts where the white substance has separated from it. 2.

A part where the white substance is interrupted. 3. Axis projecting beyond the broken end of the tube. 4. Part of the contents of the tube escaped.

Fig. 27.

Gelatinous Nerve-fibres.

(a and b magnified 340 diameters, after

Dr. Todd, Art. Nervous Centres, in Cyclop. of Anat. and Phys., Pt. xxvi., p. 707; and The Physiological Anatomy and Physiology of Man, p. 208, London, 1845.