GENERAL STRUCTURE OF THE RESPIRATORY ORGANS. 379 



oxysm of hysteric laughter may be cut short by clashing a glass of cold water 

 in the face. It seems not improbable that even the sympathetic nerve, which 

 derives many fibres from the cerebro-spinal system, and which especially 

 communicates with the pneumogastric nerves, may be one of the exciters to 

 this function ; and this perhaps not only through its ramifications in the 

 lungs, which are considerable, but also by its distribution on the systemic 

 vessels; so that it may convey to the spinal cord the impression of imper- 

 fectly arterialized blood through these, such as the pueumogastric is be- 

 lieved to transmit from the lungs. 



209. The motor or " efferent" nerves concerned in the function of Respi- 

 ration, are those which Sir C. Bell has grouped together in his " respiratory 

 system." The most important of these, the Phrenics, arise from the upper 

 part of the Spinal Cord ; the Intercostals much lower down ; whilst the 

 Facial Nerve and the Spinal Accessory, to the latter of which, as will be 

 shown hereafter (chap, xiii, sec. 2), the motor powers of the Pneumogastric 

 are chiefly due, take their origin in the Medulla Oblongata itself. M. 

 Browu-Sequard 1 has paid particular attention to the rhythmical movements 

 of the Diaphragm in Rabbits, which are observed to occur after section of 

 the phrenic nerves, and even after destruction of the entire spinal cord. 

 He attributes them to the minute ganglia described by Rouget, which are 

 found on the filaments of the phrenic nerve. It is very remarkable that 

 after such serious injury to the nervous system the two sides of the dia- 

 phragm, which are chiefly connected by tendon, should act synchronously ; 

 and also that the iuspiratory movements of the Diaphragm should regularly 

 alternate with those of the expiratory muscles, which in Rabbits are chiefly 

 the external oblique muscles of the abdomen. 



300. That the respiratory movements, as ordinarily performed, are essen- 

 tially independent of the Will, appears not only from our own consciousness, 

 but also from cases of paralysis ; in some of which the power of the will 

 over the muscles has been lost, whilst the movements have been kept up by 

 the reflex action of the Medulla Oblongata or respiratory ganglion ; whilst 

 in others, some of the respiratory muscles have been motionless during ordi- 

 nary breathing, and yet have remained under the power of the will. 2 That 

 consciousness is not a necessary link in the chain of causes which produce 

 the respiratory movements, we are enabled to judge from the phenomena 

 presented by the human being in sleep and coma, by aneucephalous foetuses, 

 and by decapitated animals. This conclusion is confirmed by a case recorded 

 by Dr. H. Ley, 3 who had under his care a patient in whom the pneumo- 

 gastrics appeared to be diseased; the lungs suffered in the usual way in con- 

 sequence, and the patient had evidently laborious breathing ; but he dis- 

 tinctly said that he felt no uneasiness in his chest. The experience of every 

 one informs him, however, that the Respiratory movements are partly under 

 the control of the will, though frequently uurestrainable by it. In ordinary 

 circumstances, when the blood is being perfectly aerated, and there is a suf- 

 ficient amount of arterial blood in the system to carry on the functions of 

 life for a short time, we can suspend the respiratory actions during a few 

 seconds without any inconvenience. If, however, we endeavor to prolong 

 the suspension, the stimulus conveyed by the excitor nerves to the Medulla 

 Oblongata becomes too strong, and we cannot avoid making inspiratory 

 efforts ; and if the suspension be still further prolonged, the whole body 

 becomes agitated by movements which are almost of a convulsive nature, 



1 Brown Sequard, Journal de la Physiologic, t. ii,'p. 115. 



2 Such cases are mentioned by Sir C. Bell, in the Appendix to bis work on the 

 Nervous System of the Human Body. 



3 On Laryngismus Stridulus, p. 417. 



