721L 



PHYSIOLOGY OF THE NERVOUS SYSTEM. 



muscular coat of the bladder are the usual 

 means by which the action of this viscus is 

 promoted. It is possible that, as with the rec- 

 tum, under peculiar circumstances the physical 

 stimulus acting reflexly on the muscular hbres 

 themselves may come in aid of that of volition ; 

 but such a mode of action is not the ordinary 

 one. A line of argument similar to that which 

 disproves the reflex nature of the action of 

 the sphincter ani tells equally against that of the 

 sphincter vesica:. Were the action of this mus- 

 cle reflex, it ought to remain perfect when- 

 ever a sufficiently large segment of the cord 

 remains in connexion with the bladder. Now 

 when the spinal cord is severed in any region 

 so as to occasion paralysis of the lower extre- 

 mities, there is almost always incontinence of 

 urine from the removal of voluntary influence 

 from the sphincter vesicse : such ought not to 

 be the case, if Dr. Hall's views were correct. 



Respecting the cardia and the valvula coli, I 

 shall only remark that the evidence of reflex 

 action is extremely defective. The cardia, in- 

 deed, has no sphincter; it is closed by the 

 lower circular fibres of the oesophagus, which 

 keep that canal in a contracted state by their 

 tone or passive contraction. The pylorus is 

 provided with a sphincter muscle of great 

 power, which closes that orifice by its passive 

 contraction, and which in animals recently 

 killed will continue to close the orifice as long 

 as the muscle retains its tone. If an animal 

 be killed during stomach digestion, the stomach 

 may be removed, and yet the pylorus will retain 

 the food in it even against gravity ; the cardia, 

 if a sufficient portion of the oesophagus be 

 retained, will resist the escape of the food ; 

 but, from the absence of a true sphincter, to a 

 much less degree than the pylorus. It is im- 

 possible that, under these circumstances, there 

 could be any reflex action, as the stomach is 

 removed from its connection with the nervous 

 centre. The valvula coh appears to act simply 

 on mechanical principles. 



There is, I apprehend, no more evidence of 

 the exclusively reflex nature of the acts of 

 expulsion than of that of the acts of retention. 

 The expulsion of the faeces and that of the urine 

 are voluntary acts, aided essentially by the con- 

 tractile power of the muscular fibres of each vis- 

 cus, and perhaps, under peculiar circumstances, 

 by a physical excitant. Were this power reflex, 

 the expulsion would be no doubt much more 

 frequent and much less under control, and, 

 therefore, productive of frequent serious incon- 

 venience. The expulsion of perspiration is 

 probably effected by the simplest mechanical 

 means, the newly secreted fluid pushing before 

 it that which was previously formed. The 

 expulsion of the semen does, indeed, exhibit 

 the characters of a true reflex act; but here 

 how marked is the physical stimulus, and how 

 necessary that it should reach a certain point of 

 excitement before the action of expulsion re- 

 sponds to it! As to the expulsion of the foetus 

 in parturition, while I am willing to admit 

 that the physical power of the cord excited by 

 the sensitive nerves at the neck of the uterus 

 may exercise some influence on the contrac- 



tions of the uterus, it seems to me quite evi- 

 dent that the actions of this organ are reflex 

 only to a very slight degree. In the first place, 

 anatomy teaches us that the muscular parts of 

 the uterus have a very trifling connexion with 

 the spinal cord ; the nerves distributed to it 

 being few, and these only partially derived 

 from the spinal cord. Secondly, parturition 

 may take place even when the spinal cord has 

 been diseased or divided so as to cut off its in- 

 fluence upon the inferior half of the body. 

 Thirdly, it has lately been ascertained that in 

 women under the influence of ether, the act of 

 parturition may take place with vigour, although 

 the nervous power have been very considerably 

 depressed by the influence of that agent. 



The immediate agent of expulsion in defee- 

 cation, micturition, and parturition is the inhe- 

 rent contractility of the muscular coat of the 

 proper organ. Being hollow muscles, the sti- 

 mulus of distension is well adapted to excite 

 them to contract. The will exercises consider- 

 able power in defalcation and micturition, 

 both upon the muscular fibres of the viscera 

 themselves, and on the abdominal muscles. 

 In parturition the voluntary contraction of these 

 latter muscles may give some assistance, but 

 the main force of expulsion is due to the con- 

 traction of the uterine muscular fibres. In all 

 the three actions, however, the influence of the 

 muscular fibres of the viscera respectively en- 

 gaged may be materially promoted by the con- 

 tractions of the abdominal muscles, which are 

 partly voluntary and partly reflex, being excited 

 by the pressure of the mass to be expelled on 

 the sensitive nerves in the neighbourhood, 

 which, acting on the spinal cord, stimulate the 

 muscular nerves, and through them cause the 

 muscles they supply to contract, in harmony 

 with the muscular tunic of the expelling viscus, 

 rectum, bladder, or uterus, as the case may be. 



I may here remark, that whilst it is suffi- 

 ciently evident that expulsion of the semen is a 

 physical or reflex act, it cannot be admitted 

 that erection of the penis is essentially so in its 

 ordinary mode of production. This act is one 

 of emotion a simple emotion of the mind is 

 sufficient to develope it: it may, however, be 

 developed by the application of a stimulus to 

 the penis or scrotum, when it clearly partakes 

 of the character of a reflex act, although even 

 under these circumstances it would be incor- 

 rect to'say that emotion had no influence in its 

 production. It is well known, however, that 

 in cases where the spinal cord has been severely 

 injured, severed indeed, by fracture and dis- 

 placement of some of the vertebrae, erection of 

 the penis may be produced, although the organ 

 is insensible, and the influence of the mind over 

 the lower half of the body is suspended, and 

 that even a slight stimulus, as the friction of 

 the bedclothes, or the introduction of a catheter, 

 is sufficient for this purpose. This is clearly a 

 purely reflex act, wholly independent of sensa- 

 tion or emotion ; but it may be likewise pro- 

 duced or kept up by the irritated state of the 

 cord itself. The painful erection of the penis, 

 called cltordec, which occurs incases of inflam- 

 matory gonorrhoea, is partly a reflex phenome- 



