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Woorara

    Abstract

    NOTWITHSTANDING the deference with which every statement that Claud Bernard has made ought to be treated, it seems probable that he was mistaken in his ideas regarding the effect of woorara on sensory nerves. The indications of sensibility under the action of woorara are afforded by the limb of a frog to which the poison has not had access, so that the endings of the motor nerves in it are not paralysed. On pinching a portion of the skin anywhere in such an animal, even on the poisoned leg, it is noticed that movement takes place only on the unpoisoned one, while all the poisoned parts remain perfectly limp and motionless. But this movement, while it might indicate pain, does not necessarily do so, and may only indicate simple reflex action. The difference between these two conditions, in which the movement is alike, is that which exists between the effect of tickling the sole of the foot in man with a feather and running a pin into it. In both cases the foot would be drawn up, perhaps even more so with the feather than with the pin, but the pin would cause pain, and the feather would not. The movement of the frog's leg in woorara poisoning much resembles that caused by the feather, for it will occur as readily, or more so, if the brain has been removed. We know that in cases where the spinal cord has been broken by accident in man reflex occurs in the legs quite readily, but of this the patient himself is utterly unconscious excepting by seeing the movements in the same way as a bystander. Increased movement, therefore, in the curarised frog, instead of indicating increased sensibility to pain, may only indicate increased irritability of the spinal cord and in all probability does so. The same arguments which would prove that woorara increases the susceptibility to pain prove also that morphia does so, for in small doses morphia also increases the movement of the leg of the frog in the same way as woorara; but we know perfectly well from observation in man that morphia does not increase pain even in small doses, and that a large dose completely abolishes it. There can be little doubt that large doses of woorara also abolish sensibility as well as motion, for after the poison has acted awhile, the movements, even in the protected leg, become less and less, showing that the spinal cord has been paralysed; but before this take place, the sensory nerves themselves are paralysed by the poison, as was first shown by Schiff, the correctness of whose experiments has been since confirmed. The mode of experiment will be better understood by reference to the accompanying diagram representing a frog, in which the artery going to one leg has been tied so as to protect it from the influence of the poison. This leg has been left unshaded, but all the poisoned parts of the body are shaded. At first, pinching in any part of the body, whether poisoned or not, will induce movement in the non-poisoned leg, but after a little they do not, while pinching of the skin of the unpoisoned leg below the point of ligature will cause movements. This is most strikingly seen when the skin is pinched, first just above the ligature, and afterwards just below it. The pinch above the ligature produces no effect; the pinch below it produces movement. In the former case the sensory nerves have been poisoned by the woorara; in the latter case they have not. This experiment shows clearly that the ends of the sensory nerves are also paralysed by woorara like the ends of the motor nerves, although they are not so quickly affected, for a reference to the diagram will show that the trunks of both motor and sensory nerves and the spinal cord have been equally exposed to the poison, and that the only difference between the skin just above the ligature and just below it is that the ends of the sensory nerves above it have been poisoned, and those below it have not been poisoned. It is therefore almost certain that woorara in large doses diminishes, and finally abolishes all susceptibility to pain, as well as all power of motion, and that it may be looked upon as an anæsthetic, although not so powerful as chloroform, ether, or morphia.

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