OF THE RESPIRATORY MOVEMENTS. 381 



sired to prolong the life of the animal after this operation, by making an 

 opening into the trachea. Dr. Reid further ascertained, that the applica- 

 tion of a stimulus to the inferior laryngeal nerves, \vhen separated from the 

 trunk, would occasion distinct muscular contractions in the larynx ; whilst a 

 corresponding stimulus applied to the superior laryngeal occasioned no mus- 

 cular movement, except in the crico-thyroid muscle. But when the superior 

 laryngeals were entire, irritation of the mucous surface of the larynx, or of 

 the trunks themselves, produced contraction of the glottis and efforts to 

 cough ; effects which were at once prevented by dividing those nerves, and 

 therein' cutting off' their communication with the Medulla Oblongata. The 

 observations of Dr. Reid have been fully corroborated by those of Rosen- 

 thai, 1 who found in addition that moderate irritation of the Vagus caused 

 increased frequency of the respiratory movements, and strong irritation, in- 

 spiration-tetamis, whilst if the superior laryngeal nerves were carefully iso- 

 lated and stimulated with weak induction currents, the respirations fell in 

 frequency, chiefly in consequence of the prolongation of the pause; and if 

 the strength of the current were somewhat increased, complete relaxation of 

 the diaphragm occurred, and expiration-tetanus. The strength of the cur- 

 rent to produce these effects must, however, be much less considerable than 

 is required to produce increase of respiratory activity and tetanus of the 

 diaphragm, when applied to the trunk of the Pueumogastric, on account of 

 the extreme sensibility of the superior laryugeal nerve. The inhibitory in- 

 fluence upon the respiratory function, and especially upon the movements 

 of the diaphragm, thus attributed by Rosenthal, to the superior laryngeal 

 branches of the Pneumogastric nerve, is so far different from that of the Car- 

 diac and Splanchnic branches of the same nerve whose controlling power 

 over muscular movements has been already alluded to ( 244, 95) that it 

 acts ceutripetally on the Medulla Oblongata, and not, like them, centrifu- 

 gally. There can be no doubt- then, that the superior and inferior laryngeal 

 branches constitute the circle of incident and motor nerves, by which the 

 aperture of the glottis is governed, and by which any irritation of the larynx 

 is made to close the passage, so as to prevent the entrance of improper sub- 

 stances; whilst the superior laryngeal nerve also excites the muscles of ex- 

 piration, so as to cause the violent ejection of a blast of air, by which the 

 offending gas, fluid, or solid, may be carried off. The effect of carbonic 

 acid in causing spasmodic closure of the glottis is well known ; and affords 

 a beautiful example of the protective office of this system of nerves. The 

 mucous surface of the trachea and bronchi appears from the experiments of 

 Valentin, to be endowed with excitability, so that stimuli applied to it pro- 

 duce expiratory movements; and this evidently operates through the branches 

 of the pneumogastric distributed upon the membrane. Here, as elsewhere, 

 we find that a stimulus applied to the surface has a much more decided in- 

 fluence than the irritation of the trunk of the nerve supplying it. 



303. The actions of sighing, yawning, sobbing, laughing, coughing, and 

 sneezing, are nothing else than simple modifications of the ordinary move- 

 ments of respiration, excited either by mental emotions, or by some stimulus 

 originating in the respiratory organs themselves. Sighing is nothing more 

 than a very long-drawn inspiration, in which a larger quantity of air than 

 usual is made to enter the lungs. This is continually taking place to a 

 moderate degree ; and we notice it particularly when the attention is re- 

 leased, after having been fixed upon an object which has excited it strongly, 

 and which has prevented our feeling the insufficiency of the ordinary move- 



1 Rosenthal, Die Athembewogungen und ihren Beziehungen zum Nerv. Viigiif, 

 Berlin, 18(i2; and Arehiv f. Anat. und Physiol., 1852, p. 22(j. 



