and

nerve-cells. The influence is exerted through the motor nerves, indeed consists in the normal integrity of the fibres (see p. 24). The nutrition of the bones and joints is also under the control of the cord, and probably is exerted through the posterior roots. It is true, the growth of the bones is hindered when the anterior cornua are diseased, but no atrophic change seems then to occur in the osseous structure, and the influence of the paralysis may be indirect. A true trophic change, and an alteration in the joints, may occur in locomotor ataxy, in which the disease is of the posterior nerve-fibres.

The nutrition of the skin seems also to depend on nerves that have their course in the posterior roots. The clearest fact is that irritation of the nerve-structures has far more effect than simple loss of function. It is when the cord or nerve-roots are the seat of irritative inflammation that the most acute trophic changes occur, while mere degeneration of these nerves induces slower and slighter changes (see p. 22). VISCERAL CONTROL.-Although the viscera are under the immediate control of the sympathetic system of nerves, they are related to centres in the spinal cord, and it is from these centres that the controlling influence is really derived, probably by means of the finer fibres of the anterior roots. The relation is the most direct and important, so far as concerns the diseases of the spinal cord, in the case of the organs over which the will has an influence, the rectum and the bladder. The centres for these are in the lumbar enlargement, but we do not know their exact position. They are probably complex reflex centres. We can best understand their action by studying them when voluntary influence is lost.

The centre for the sphincter ani is the more simple, but the system of action of each is probably similar. In the wall of each viscus we have muscular fibres to expel the contents, and at the mouth a sphincter arrangement to prevent continuous evacuation. Fæces or air in the rectum, and urine in the bladder, may excite the lumbar centre, and cause two effects-contraction in the wall and relaxation of the sphincter. This process can be controlled by the will to a considerable extent, although we are still ignorant of the precise mode in which the voluntary influence is exerted. But if the volitional path in the cord is interrupted above the lumbar centres, the will can no longer control the reflex processes; as soon as fæces irritate the rectum, they are expelled by the reflex mechanism; as soon as a sufficient quantity of urine accumulates in the bladder, a reflex contraction of the detrusor and relaxation of the sphincter cause its escape. The affection of the voluntary path for the sphincter is not always proportioned to that for the legs. If the damage to the cord involves also the sensory tract, the patient is unconscious of the action of the bladder or bowel. If the sensory tract is unaffected, the patient is aware of the process, but cannot control it. It is often said that there is permanent relaxation of the sphincters, but this is true only when the lumbar centres are inactive or destroyed. In this condition evacuation occurs as soon

bladder

as fæces or urine enter the bowel or rectum. The urine escapes continuously, instead of being expelled at intervals. The condition is less obvious in the case of the rectum, because there is no such continuous passage of fæces into the rectum as there is of urine into the We may, however, distinguish between the two states of the rectum by the introduction of the finger. If the lumbar centre is inactive, there is a momentary contraction, due to local stimulation of the sphincter, and then permanent relaxation. If, however, the reflex centre and motor nerves from it are intact, the introduction of the finger is followed, first by relaxation, and then by gentle, firm, tonic contraction. I have verified this by introducing an india-rubber cylinder instead of the finger, and registering the pressure on the cylinder by connecting it with a recording apparatus. The relaxation is then found to be preceded by a very slight brief contraction, and to be followed by unbroken tonic contraction. The relaxation may also be readily produced by any impression on the mucous membrane above the sphincter. Fig. 83 shows some of the tracings obtained.

FIG. 83.-TRACINGS OF THE ACTION OF THE SPHINCTER ANI.
The vertical lines represent seconds of time.

1. Effect on contraction of sphincter of the injection into the rectum of a small quantity of air at . a, fall in pressure due to the inhibition of the contraction; b, rise due to the slowly returning contraction. 2. Effect of the introduction of the instrument. a, sudden rise of lever at moment of introduction, due to the exposure of the instrument to the pressure of the sphincter (the top of this line represents the degree of previous contraction); b, initial rise due to increased contraction; c, fall from partial inhibition; d, subsequent contraction, rising to a greater degree than the initial contraction, and subsequently falling slightly. 3. Effect of cough. a, pressure of tonic contraction of sphincter (the slight irregularities are due to pulse-waves); b, fall in pressure, due to the movement of the instrument by the cough; c, initial contraction; d, relaxation of inhibited sphincter; e, e, e, rhythmical variations in subsequent rise. (From the Proc. Royal Society,' 1877.)

The action of the bladder mechanism can be best understood by assuming that the motor centre really consists of two parts, one (MS, Fig. 84) maintaining the contraction of the sphincter, the other (MD) exciting the contraction of the detrusor fibres, and that these two parts are antagonistic; when one acts the other is inhibited. Thus,

tions.-The activity of ans depends on the inreflex loop to and from entre, also situated in the rgement, but the due action 're depends on cerebral as well as on reflex influences. the centre, or of the nerves or from it, abolishes sexual e sexual reflex is, however, shares the condition of these

3

saction is impaired by interse higher up, the connection d, the sexual act cannot be the controlling centre (p. 20)

is unimpaired, the refiex sexual processes are not in excess, and may even be diminished; but if the path from this controlling centre is also interrupted, the reflex sexual processes are in excess like the other superficial reflexes, and priapism results. If the reflex centre, or connecting paths, are partially diseased, the sexual process may be impaired and imperfect, but not abolished.

Vaso-motor Centres.-The sympathetic nerves to the vessels are influenced from the spinal cord. It is probable that the path is by the fine fibres of the anterior roots, and that most of the dilator fibres leave the cord between the third dorsal and the second lumbar, and most of the constrictor fibres from the seventh dorsal to the first lumbar. Some facts of disease suggest that the centres are situated in the intermediate grey matter; and this conclusion is supported by the important researches of Gaskell, which refer the function to the small cells of the intermedio-lateral tract, which he traces upwards to the vasomotor centre in the medulla. The action of the vaso-motor nerves may be deranged by disease of the cord. It is probable that such a relation exists between all parts of the vaso-motor system of nerves and the cord, and that the relation obtains between each segment of the cord and the vascular nerves to the corresponding part of the trunk and limbs. This derangement in disease may take a part in the production of the changes in nutrition, but it is probably not the sole mechanism by which these changes are produced.

There is a special connection between the sympathetic and the cervical region of the spinal cord. This region contains the path to the visceral nerves that control the sugar-forming functions of the liver. The lower part of the cervical enlargement contains also an important centre which controls the sympathetic nerves for the vessels of the head and face. The path of central influence for the radiating fibres of the iris passes also from the region of the third nerve nucleus, down the cervical cord, by the lowest cervical or first dorsal nerve, to the sympathetic, and then ascends the cervical trunk, and passes along the fibres which accompany the internal carotid artery to the ciliary ganglion. Fibres also pass from the cervical cord to the sympathetic, through which the action of the heart is accelerated.

MUTUAL RELATION OF THE FUNCTIONS OF THE SPINAL CORD.— It may be well to present, in the form of a table, the relation of the several functions of the cord, motor, sensory, and reflex, as far as our knowledge of these relations extends. Many points are still uncertain; these have been, for the most part, omitted. The table does not need any detailed explanation. It is merely a comparative collection of the facts that have been stated in the preceding pages. We shall find the value of this collocation of functions when we consider the effects of transverse lesions of the cord at different levels.

VOL. I.

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Table showing the approximate relation to the spinal nerves of the various motor, sensory, and reflex functions of the spinal cord.