C.—Action on Centres of Cranial Nerves.
Among the symptoms denoting paresis of motor-centres of cranial nerves, together with sympathetic ganglia, the first and most noteworthy is the early dilatation of the pupil. This truly pathognomic condition is never absent, and becomes intense when paresis becomes intensified into paralysis. The most glaring light, in immediate proximity to the eyeball, has then no effect whatever on the pupil. If it remains dilated after strychnine injections have restored consciousness and the power to walk, it is a sure sign that the snake-poison is not completely counteracted, and will in all probability re-assert itself, necessitating another injection, whilst a pupil restored to its normal condition justifies the conclusion that the patient is safe.
Another symptom denoting paresis of the cranial nerve-centres is a marked change in the expression of the face. The features become relaxed, and lose their mimetic play. The cornea is dull, and, together with the anterior surface of the eyeball, becomes dry, as the eyelids are moved imperfectly, if at all, and the tears in consequence are not properly distributed over the conjunctiva. The nostrils become more or less immovable, and the naso-labial fold is obliterated, whilst the lower lip hangs down. The lips are apart, as the lower jaw is not held up by the muscles. When paralysis supervenes it drops entirely, and the tongue protrudes.
Deglutition, somewhat difficult in paresis, is completely suspended in the paralytic stage, through paralysis of the soft palate, the pharynx, and œsophagus. Liquids forced on the patient in this extremity may partly flow down the œsophagus, but will also enter the larynx, and their administration should be carefully avoided.
D. Action on motor-centres of Cerebellum and Basal Ganglia.
Of this action little if anything is patent to observation. A certain want of co-ordination in the movements has been noticed in the early stage of paresis, and the peculiar staggering walk of persons in this stage is probably owing to an affection of the motor-centres of the cerebellum. That they do not escape the action of the subtle poison, when symptoms denoting the invasion of all the other motor-centres throughout the body are in evidence, we have every reason to assume. The co-ordination and automatic regulation of the lower motor-centres must necessarily escape observation when the function of these centres is partially suspended, and when, moreover, the powerful currents of nerve force the cerebellum and basal ganglia receive from the motor cortical centres of the cerebrum are partially if not wholly withdrawn.
E. Action of the Motor Cortical Centres of the Cerebrum.
In all but the very lightest cases of snakebite-poisoning there are always symptoms manifested that cannot be referred to any other cause than an invasion of the centres now under consideration. They range from mere stupor, confusion of thought and delirium to the deepest coma, with complete extinction of consciousness and insensibility to all external impressions. Coma is a frequent and in serious cases an almost invariable symptom in Australia. After the bite of our death adder only we find persons sometimes collapse and expire suddenly, when still conscious and able to answer questions rationally. Coma invariably develops from sleep. It is, in fact, sleep intensified. An almost irresistible desire to sleep is one of the first symptoms to be observed. If the dose of poison imparted by the snake has been small, the desire may pass off or the sleep may not assume the form of coma, but in all serious cases it quickly assumes that form. Vice versa the deepest coma becomes sleep again, when the suspended function of the cortical centres is roused by strychnine injections. The insensible and completely paralysed patient usually announces the gradual return of consciousness by a few groans and uneasy movements and not unfrequently begins to snore, as in ordinary sleep, when a smart shake at the shoulder will rouse him into full consciousness. At other times this transition from coma back to sleep does not take place and consciousness returns quite suddenly, the persons opening their eyes and looking around them, dazed and bewildered, but perfectly conscious at once. When coma is fully established and the largest and most powerful motor-centres have succumbed to the insidious poison, general paresis becomes general paralysis and all the motor-centres of the body are in a condition of more or less suspended functional activity. This and this only is the condition of the centres, the whole secret of snake-poison, that has puzzled the human mind for ages and yet appears so simple when discovered at last. It is beautifully and strikingly illustrated in the phenomena before us. We have coma and complete general paralysis, every motor-nerve cell, from the highest psycho-motor one downwards, is thrown into a state of torpor and has ceased to discharge the life force that regulates every process of life and the entire absence of which inevitably must be death. Only weak, lingering currents are sent forth yet and put off the inevitable finale for a time. But the strychnine is injected and mark the change. It courses quickly to every one of the sleepers, for whom it also has an affinity, but the direct opposite to that of the deadly venom that has overpowered them. It touches them as if with the wand of a magician and orders them to awake and do their work. There is no disobeying the mandate, for it is founded on one of nature's unchangeable laws. Almost immediately the cells begin their work again, the life streams flow afresh, coma and paralysis vanish and within a very short time the subject of this beautiful experiment is snatched from the brink of the grave and restored to life and health.
The phenomena of sleep and coma as the result of a poison acting as a depressant of motor nerve force afford food for some interesting speculations, which, however, as more concerning the psychologist, the writer can only glance at here. It is evident that in the highest of psycho-motor centres, the organs of thought and of consciousness, the paresis of the lower centres assumes the form of sleep, and paralysis that of coma. Sleep, as a partial, and coma, as a complete, obliteration of thought and consciousness must, therefore, be intimately connected with motor nerve function, sleep being a reduction, coma a suppression of the function, or a suspension of thought. Ideation, to use J. S. Mill's very appropriate term for the thought process, appears to be effected by motor nerve currents or, at all events, to be accompanied by them and suspended with their suspension. The thinking principle, the nous within us, is no doubt more than mere nerve action, but it can, apparently, not manifest its presence without motor nerve cells in healthy action. Every thought, though not synonymous, is evidently synchronous with a current of motor nerve force, and it is not improbable that, by means of these currents, that silent transference of thought is effected from brain to brain, which modern psychology has demonstrated to be not only possible but actual under certain conditions. But further speculation on these interesting mysteries it would be out of place here to indulge in.