REFLEX CHARACTER OF RESPIRATORY MOVEMENT. 381 



that the presence of venous blood in the arterial capillaries of the 

 system, and the consequent stagnation in the current through them 

 ( 597), may exert an influence through the Sympathetic nerves : which 

 may be transmitted, by the copious inosculations of that system with 

 the Par Vagum, to the Medulla Oblongata; and which, may there serve 

 as a valuable auxiliary in exciting the respiratory movements. 



687. Of the mode in which the impressions, thus transmitted to the 

 Medulla Oblongata, act in exciting the motor impulses which issue 

 from it, nothing is known; but these impulses, directed along the 

 phrenic, intercostal, and other nerves, produce the requisite movements. 

 When the stimulus is unusually strong, various nerves and muscles 

 are put in action, which do not co-operate in the ordinary movements 

 of inspiration ; and it may sometimes be observed, that movements are 

 thus excited in parts, which will not act in obedience to the will, being 

 to all appearance completely paralysed. This fact shows how com- 

 pletely the class of actions in question is independent of the influence of 

 the mind; but we must not lose sight of the control which the mind, 

 especially in the higher classes of animals, possesses over them. Va- 

 rious actions of the respiratory muscles, particularly those of weeping 

 and laughing, are the most direct means of expressing the passions and 

 emotions of the mind ; and are involuntarily excited by these. And, 

 again, the respiratory actions are placed in a certain degree under the 

 control of the Will ; in order that they may be subservient to the pro- 

 duction of vocal sounds, and to the actions of speech, singing, &c. The 

 will cannot long suspend the respiratory movements ; for the stimulus 

 to their involuntary performance soon becomes too powerful to be any 

 longer resisted. And it is well that it should be so ; for if the perfor- 

 mance of this most important function were left to our own choice, a 

 few moments of forgetfulness would be productive of fatal results. But 

 it is to the power which the will possesses, of directing and controlling 

 the respiratory movements, that we owe the faculty of producing arti- 

 culate sounds, and thus of holding the most direct and intimate con- 

 verse with each other. 



688. It is essential for the due performance of the respiratory move- 

 ments, that the portion of the nervous centres, on which they depend, 

 should be in a state of activity. This is the case, under ordinary cir- 

 cumstances, throughout life. The state of perfect quiescence, to which 

 the Brain is liable, never affects the Medulla Oblongata ; and the respi- 

 ratory movements are consequently kept up with as much regularity 

 and energy (in proportion to the requirements of the system), during 

 our sleeping, as during our waking hours. But if any cause induce 

 torpidity of the medulla oblongata, the respiratory movements are then 

 retarded, or even suspended altogether ; and all the consequences of 

 the cessation of the aeration of the blood speedily develope themselves 

 ( 706). This is seen in apoplexy ; when the pressure, or other cause 

 of suspended activity, which at first affected the brain alone, gradually 

 propagates its influence downwards. The same is the case in narcotic 

 poisoning ; in which also the brain is the first to be affected, and may 

 suffer alone ; but if the noxious influence be propagated to the medulla 

 oblongata, it manifests itself in the retardation of the respiratory move- 



