338 PULMONARY MUCOUS TISSUE. 



become slow and feeble, as in the case of an animal whose 

 skin is covered with varnish ; the temperature of the body is 

 lowered, and is only kept up by the influence of the will upon 

 respiration. Here it is plain that one of the sources, the 

 cutaneous source, if we may so speak, of the respiratory reflex 

 system has been withdrawn, and that the influence of the 

 pneumo-gastric nerve alone is not sufficient to excite the 

 action of the central nervous system. The will supplies this 

 lack of external influence, until the unfortunate patient con- 

 demned to this extraordinary species of suffering, at length 

 yields to his fatigue, and falls asleep. Respiration then be- 

 comes so feeble that the temperature of the body is consider- 

 ably lowered, and death finally ensues. 1 



The function of the skin, in regard to respiration, is also 

 demonstrated by a number of medical practices, which are 

 very common, and consist in exciting the respiratory move- 

 ments by means of irritants applied to the skin: such as fric- 

 tion, effusions of cold water, cauterization, and the more for- 

 cible methods sometimes employed to restore life in persons 

 apparently drowned, as well as those employed to excite, in 

 a new-born infant, the first movement of inspiration, which is 

 sometimes delayed and performed with difficulty. 



3. Centrifugal l*aths. It is scarcely necessary to mention 

 the centrifugal path of the respiratory reflex system here : 

 anatomy sufficiently proves that this is along motor nerves 

 which leave the cervical and dorsal parts of -the spinal cord 

 in order to join the muscles of the walls of the thorax; we 

 will only mention, as being the most remarkable, the phrenic 

 nerve ; this leaves the cervical plexus, and innervates the 

 diaphragm ; by means of sections of the spinal cord at some 



1 As the pneumo-gastric nerve alone is powerless to excite res- 

 piration when the impressions made by the cutaneous nerves are 

 withdrawn, so these nerves are unable of themselves to keep up the 

 reflex action when the pneumo-gastric nerves are cut. The death 

 of animals whose vagi nerves have been divided must, no doubt, be 

 ascribed to this cause. Physiologists have sought to discover in 

 the stomach, in the heart, and the lungs the cause why death so 

 inevitably follows this operation. It has been proved by numerous 

 experiments that the lungs are principally affected; since animals 

 whose two pneumo-gastric nerves have been cut, have been fre- 

 quently observed to die in a few days, and since the autopsy showed 

 that the lungs were not impaired, death in these cases should be 

 ascribed to the suppression of the sensory or centripetal filaments 

 of the pneumo-gastric nerves. (See Paul Bert, " Legons sur la 

 Physiologic cornparee de la Respiration," p. 496.) 



