Licence: Public Domain Mark
Credit: Physiology of the nervous system / by Robert B. Todd. Source: Wellcome Collection.
Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.
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![is wholly independent of the nervous system, and is effected partly by the forcible injection of the fluid into the vagina and uterus, and partly by the ciliary movement of the sperma- tic particles, the so-called spermatozoa. Tlie acts of retention cannot certainly be re- garded as wholly reflex. Taking the instances quoted by Dr. Marshall Hall, the action of the sphincters, we shall find but little evidence in support of his view. The sphincter ani, the most perfect and complete of the sphincters, is « voluntary muscle, endowed with a high de- gree of contractile power; its circular form renders it very prone to act under the stimulus of distension, and it therefore resists any dis- tending force, whether from above or below. This resistance, however, is powerfully in- creased by voluntary effort, as on the other hand it is materially diminished if the muscle be separated from cerebral influence. The ha- bitual closed state of the anus, during the quiescence of the rectum, is effected by the tone or passive contraction, which requires for its perfect developement only that the muscle should enjoy a healthy nutrition. As long as this remains, the sphincter closes the orifice of the rectum sufficiently to prevent the escape of a small quantity of matter from it; this power, however, does not enable it to resist any consi- derable pressure; such resistance can only be effected by the active contraction of the muscle, effected partly by the stimulus of distension, and partly and chiefly by volition. The voluntary nature of the actions of the Sj)hincter is obvious from the personal feelings of each individual. It is also sufficiently in- dicated by the fact that if the spinal cord be divided in any region by disease or injury, so as to induce com|)lete paralysis of the lower extremities without muscular rigidity, the sphincter will be paralysed, however extensive the inferior segment of the cord may be. Were its actions entirely or even chiefly of the reflex kind, the continuance of the lower segment of the cord in the healthy state ought to preserve their integrity. But this is never the case ex- cepting in the rare instance of a persistent state of irritation of the inferior segment of the cord sufficient to maintain rigidity of the mus- cles of the lower limbs, and also to provoke a continued state of active contraction. It is, however, possible that a physical stimu- lus applied to the mucous membrane of the rectum or anus may excite by reflex action the contraction of the sphincter, and thus come in aid of voluntary power, and of the inherent contractility of the muscle; but such aid is called forth only under peculiar circumstances, and either not at all or to a very trifling extent in the ordinary action of the sphincter. More- over, in deep-seated and extensive lesion of the brain, paralysis of the sphincter ani is a constant symptom, the spinal cord being per- fectly healthy, and the reflex actions of the paralysed lower extremity (for in such cases the paralysis is generally hemiplegic) well marked. Such cases must be regarded as affording the most conclusive evidence against the reflex nature of the action of the sphincter ani, and all the facts that I have mentioned denote abundantly that the reflex action of the sphincter ani is the exception and not the rule. The experiments which Dr. Hall adduces in support of the reflex nature of the action of the sphincter are inconclusive for this purpose. They consisted in the division of the spinal cord in a horse and a turtle, and the excitation of re- flex actions immediulcly afterwards. If the ex- periment be repeated in a dog, the following re- sult will be observed: immediately after the division of the cord the sphincter will contract repeatedly without the application of any new stimulus, and the dog will raise and depress his tail, and these phenomena will continue as long as the irritation produced in the cord by the section remains. When this irritated condition shall have passed off’, the experimenter will find it impossible to excite the action of the sphincter muscle by stimulating the anus. If the actions of this muscle were of the reflex kind, surely they ought to continue as long as the segment of the cord with which its nerves are connected shall retain its powers intact. A remarkable degree of sensibility exists in the cutaneous covering of the verge of the anus in most animals, which is calculated to mislead with reference to the reflex nature of the action of the sphincter. In the decapitated frog, sti- mulation of the anus excites forcible extension of the posterior extremities. Mr. Grainger de- scribes a phenomenon which was noticed by Professor Bischoff in the green frog (Rana ar- boreu), so common in many parts of Germany. “ Upon irritating the cloaca in one of these animals which had been decapitated, the most violent emotions were excited in the hind legs, and repeated attempts were made by these limbs to remove the instrument with which the cloaca was touched. This fact,” adds Mr. Grainger, “ I have since repeatedly seen in the green and common frog, both when the head was removed and when the spinal cord was divided in the back.”* I can iidd my te.stimony to this fact, having witnessed it many times in the common frog. Dr. Hall himself, indeed, furnishes experi- mental evidence well calculated to cast a doubt upon his views of the nature of the action of the sphincter, and to indicate the existence of some source of fallacy in his experiments. Tlie subject of experiment vvas a turtle ; in one ex- periment, it is stated, “ the sphincter was per- fectly circular and closed; it was contracted still more forcibly on the application ofa stimu- lus.”f In a second experiment, he says, “if, when the cloaca is distended, the integuments over it are stimulated, the water is propelled to a considerable distance.”J Here are two op- posing actions caused by stimulation of the same region of the integument! With regard to the sphincter vesicre, or more ])roperly to the circular fibres of the muscular coat of the bladder, the influence of the will cannot be denied. Voluntary influence through the vesical nerves and the irritability of the • Grainger on the Spinal Cord, p. 59. t First Mem. ^ 37. } Second Mem. ^ 172.](https://iiif.wellcomecollection.org/image/b22332807_0031.jp2/full/800%2C/0/default.jpg)
