REFLEX RESPIRATION. 337 



excitation of the upper laryngeal nerve takes place, we find 

 it entirely relaxed ; and, from this point of view, the superior 

 laryngeal nerve may therefore be considered as a centripetal 

 moderating nerve of respiration. 



The pneumo-gastric nerve, and superior laryngeal branch, 

 are not, however, the only centripetal respiratory nerves ; 

 respiration does not cease entirely when they are cut, al- 

 though it changes its rhythmical regularity. There are other 

 sensory tracts or paths which bring the respiratory centre 

 into action, and other surfaces than the pulmonary surface 

 which serve as a starting-point to these centripetal nerves. 

 The skin and its nerves perform this office. It is impossible 

 to cut all the nerves of the skin for the purpose of experi- 

 menting on these latter centripetal conductors, but the 

 cutaneous surface may at least be preserved from all outward 

 contact, especially from that of the air or of water, this latter 

 medium appearing equally capable with the air of affecting 

 the centripetal nerves of respiration. If the skin be covered 

 with an impermeable coating, such as varnish, the respiration 

 is observed to become more feeble and slower, ceasing en- 

 tirely in some cases, and in all becoming insufficient : as a 

 sufficient quantity of oxygen is not supplied, combustion is 

 impeded, the animal grows cold, and dies ; this method is 

 frequently employed, in physiological laboratories, for the 

 purpose of changing a warm-blooded into a cold-blooded 

 animal by a slow and gradual process of chilling. Some 

 cases of accident have shown that the same thing takes place 

 in man, Avhen nearly the entire skin, or a great part of it, is 

 destroyed. In the large breweries in our towns it happens 

 but too often that a workman falls into one of the immense 

 boilers found in these establishments ; even if taken out im- 

 mediately his skin will be found scorched, and the burns, 

 though sometimes not severe, will be always of great extent, 

 and seriously modify the skin, in its nervous relations ; as is 

 always the case in regard to the sensibility of any surface of 

 which the epithelium is injured. In some cases of this kind 

 we have observed that the influence of the wiU is necessary 

 to the performance of respiration with the usual fulness and 

 intensity. The patient then breathes because he desires to 

 breathe, and as the physiological reflex action is insufficient 

 for the purpose on account of the injury to the centripetal 

 organs, the movements of the thorax no longer exhibit their 

 accustomed regularity or apparent spontaneity; if, however, 

 the patient forgets to breathe^ the movements of the thorax 



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