PHYSIOLOGY OF THE NERVOUS SYSTEM. 



72 IK 



is u holly 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. 



The 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 aui, the 

 most perfect and complete of the sphincters, is 

 a 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 

 sphincter 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 complete 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 membrana 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 immediately 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 actionofthe 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 tb.e 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- 

 borea), 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. 7 '* I can add my testimony 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. The 

 subject of experiment was 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."! Here are two op- 

 posing actions caused by stimulation of the 

 same region of the integument ! 



With regard to the sphincter vesicse, or more 

 properly 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. 



