696 OF THE FUNCTIONS OF THE NERVOUS SYSTEM. 



which are essential to its regular maintenance are performed through the inter- 

 mediation of the Spinal Axis alone ; that the Will has only such a limited 

 power over them as to bring them into harmony with its other requirements, as 

 in the acts of vocalization and in extraordinary muscular exertions ; and that the 

 stimulus by which they are commonly maintained does not even affect the con- 

 sciousness, the "besoin de respirer" only becoming sensible when the respiratory 

 process is being imperfectly performed ( 548 551). Not only are the ordi- 

 nary respiratory movements performed through this channel, but the aperture 

 of the Glottis is regulated by it in everything that concerns the respiration ; 

 and either by its spasmodic closure against the entrance of unfit substances, or 

 by the expulsor effort of coughing, which is excited by them when they do find 

 their way into the air-passages, these passages are kept free from solid, liquid, 

 or gaseous particles, whose presence in them would be injurious. In the expul- 

 sion of the Generative products, also, the reflex power of the Spinal Cord takes 

 an important share. The muscular contractions which produce the Emissio 

 Seminis are excito-motor in their nature; being independent of the Will, and 

 not capable of restraint by it when once fully excited ; and being (like those of 

 Deglutition) excitable in no other way than by a particular local irritation. It 

 has been shown by experiment, and also by pathological observation, that the 

 separation of the lower portion of the Spinal Cord from the upper does not pre- 

 vent these movements from being excited, although the act is then unaccom- 

 panied with sensation, which proves that sensation is not essential to its perform- 

 ance ; on the other hand, the power of emission is annihilated by destruction of 

 the lower portion of the Spinal Cord, or by section of the nerves which supply 

 the genital organs. The act of Parturition, however, seems to be less depend- 

 ent upon the Spinal Cord ; for, as will be shown hereafter (CHAP, xix.), the 

 contractions of the Uterus, which are alone sufficient to expel the foetus when there 

 is no considerable resistance, are not to be regarded as reflex; and it is only in 

 the co-operation of those associated muscles which come into play in the second 

 stage of labor, when the head is passing through the os uteri and is engaged in 

 the pelvic cavity, that the assistance of the Spinal cord and its nerves is called 

 in. These movements, like those of Defecation, may be to a certain extent 

 promoted or restrained by voluntary effort ; but when the exciting influence 

 (the pressure of the head against the parietes of the vaginal canal) has once 

 been fully brought into operation by the uterine contractions, the Will has little 

 power over them, either in one way or the other. The antagonizing influence of 

 the sphincter vaginae seems, like that of the sphincter ani, to be dependent 

 upon the Spinal Cord ; and thus it happens that when its tension and that of 

 other muscular parts have been destroyed by death, whilst the uterus still retains 

 its contractility, the power of the latter has sufficed for the completion of the 

 parturient process, the child being expelled after the respiratory movements 

 have ceased. 



724. The Spinal Cord is not merely the instrument whereby the movements 

 essential to the maintenance of the Organic functions are sustained; it is also 

 subservient to other muscular actions whose character is essentially protective. 

 Thus it was ascertained by Dr. M. Hall 1 that, if the functions of the Brain be 

 suspended or destroyed, without injury to the Spinal Cord and its nerves, the 

 Orbicularis muscle will contract, so as to occasion the closure of the eyelids, 

 upon their tarsal margin being touched with a feather. This fact is interesting 

 in several points of view. In the first place, it is a characteristic example of 

 pure reflex action, occurring under circumstances in which volition cannot be 

 imagined to guide it, and in which there is no valid reason to believe that sen- 

 sation directs it. Further, it explains the almost irresistible nature of the 



1 "Memoirs on the Nervous System," 1837, p. 61. 



