OF THE RESPIRATORY MOVEMENTS. 383 



of the glottis and of the larynx at its upper orifice by the approximation of 

 the epiglottis to the walls of the pharynx (Ed. Smith), at the moment when 

 expiration commences ; and 3d, in the bursting open (as it were) of the glottis, 

 by the violence of the expiratory movement ; so that a sudden blast of air is 

 forced up the air-passages, carrying before it anything that may offer an ob- 

 struction. The difference between Coughing and Sneezing consists in this, 

 that in the latter, the communication between the larynx and the mouth is 

 partly or entirely closed by the drawing together of the sides of the velum 

 palati over the back of the tongue ; so that the blast of air is directed, more 

 or less completely, through the nose, in-such a way as to carry off any source 

 of irritation that may be present there. It is difficult to say how far these 

 actions are independent of consciousness, or how far they may require the 

 stimulus of sensation for their performance. 



305. Various alterations are produced in the Lungs by section of the 

 Puenmogastric nerves ; the inquiry into the nature and succession of which 

 has been most carefully prosecuted by Dr. J. Reid j 1 aud as his results have 

 a very important bearing on several physiological and pathological questions 

 of great interest, a summary of them will be here given. In the first place, it 

 has been fully established by Dr. Reid, that section of the Vagus on one side 

 only does not necessarily, or even generally, induce disease of that lung; and 

 hence the important inference may be drawn, that the nerve does not exercise 

 any immediate influence on its functions. When both Vagi are divided, how- 

 ever, the animal rarely survives long; but its death frequently results from 

 the disorder of the digestive functions. Nevertheless, the power of digestion 

 is sometimes restored sufficiently to reinvigorate the animals; and their lives 

 may then be prolonged for a considerable time ( 92). In fifteen out of seven- 

 teen animals experimented on by Dr. Reid, the lungs were found more or less un- 

 fit for the healthy performance of their functions. The most common morbid 

 changes were a congested state of the bloodvessels, and an effusion of frothy 

 serum into the air-cells and bronchial tubes. In eight out of the fifteen, these 

 changes were strongly marked. In some portions of the lungs, the quantity 

 of blood was so great as to render them dense. The degree of congestion 

 varied in different parts of the same lung; but it was generally greatest at 

 the most depending portions. The condensation was generally greater than 

 could be accounted for by the mere congestion of blood in the vessels, and 

 probably arose from the escape of the solid parts of the blood into the tissue 

 of the lung. In some instances the condensation was so great, that consider- 

 able portions of the lung sank in water, and did not crepitate ; but they did 

 not present the granulated appearance of the second stage of ordinary pneu- 

 monia. In five cases in which the animal had survived a considerable time, 

 portions of the lungs exhibited the second, and even the third stages of pneu- 

 monia, with puriform effusion into the small bronchial tubes ; and in two, 

 gangrene had supervened. One of the most important points to ascertain in 

 an investigation of this kind, is the first departure from a healthy state ; to 

 decide whether the effusion of frothy reddish serum, by interfering with the 

 usual change in the lungs, causes the congested state of the pulmonary vessels 

 and the labored respiration ; or whether the effusion is the effect of a previ- 

 ously congested state of the bloodvessels. The former is the opinion of many 

 physiologists, who have represented the effusion of serum as a process of 

 morbid secretion, directly resulting from the disorder of that function pro- 

 duced by the section of the nerve; the latter appears the unavoidable in- 

 ference from the carefully noted results of Dr. Reid's experiments. In 

 several of these, only a very small quantity of frothy serum was found in 



1 Op. cit. 



