PNEUMOGASTRIC NERVE. 581 



in animals in which the nerve is anatomically distinct, exist in the trunk of 

 the pneumogastric. The action of the depressor nerves, which is reflex, has 

 already been described in connection with the physiology of the circulation. 



Properties and Uses of the Pulmonary Nerves. The trachea, bronchia 

 and the pulmonary structure are supplied with motor and sensory filaments 

 by branches of the pneumogastrics. The recurrent laryngeals supply the 

 upper part, and the pulmonary branches, the lower part of the trachea, the 

 lungs themselves being supplied by the pulmonary branches alone. The 

 sensibility of the mucous membrane of the trachea and bronchia is due to the 

 pneumogastrics, for these parts are insensible to irritation when the nerves 

 have been divided in the neck. Longet has shown that while an animal 

 coughed and showed signs of pain when the mucous membrane of the respira- 

 tory passages was irritated, after division of the pneumogastrics there was 

 no evidence of sensibility, even when the tracheal mucous membrane was 

 treated with strong acid or cauterized. He also saw the muscular fibres of 

 the small bronchial tubes contract when an electric stimulus was applied to 

 the branches of the pneumogastrics. 



Effects of Division of the Pneumogastrics upon Respiration. Section of 

 both pneumogastrics in the neck, in mammals and birds, is usually followed 

 by death, in two to five days. In very young animals, death may occur 

 almost instantly from paralysis of the respiratory movements of the glottis. 

 It has been found by all experimenters that animals survived and presented 

 no very distinct abnormal phenomena after section of one nerve. Accord- 

 ing to Longet, animals operated upon in this way present hoarseness of the 

 voice and a slight increase in the number of respiratory acts. Some observ- 

 ers have found the corresponding lung partly emphysematous and partly en- 

 gorged with blood, and others have not noted any change in the pulmonary 

 structure. 



When both nerves are divided in full-grown dogs, the effect upon the 

 respiratory movements is very marked. For a few seconds the number of 

 respiratory acts may be increased ; but so soon as the animal becomes tran- 

 quil, the number is very much diminished and the movements change their 

 character. The inspiratory acts become unusually profound and are at- 

 tended with excessive dilatation of the thorax. The animal generally is quiet 

 and indisposed to move. Under these conditions the number of respirations 

 may fall from sixteen or eighteen to four per minute. 



In most animals that die from section of both pneumogastrics, the lungs 

 are found engorged with blood, and, as it were, carnified, so that they sink in 

 water. This condition is not the result of inflammation of the pulmonary 

 parenchyma, although this was the view formerly entertained and is even now 

 held by some physiologists. Bernard found that the pulmonary lesion did 

 not exist in birds, although section of both nerves was fatal. It had previ- 

 ously been ascertained that in some animals death takes place with no altera- 

 tion of the lungs. When the entrance of the secretions into the air passages 

 was prevented by the introduction of a canula into the trachea, the solidifica- 

 tion of the lungs was nevertheless observed. Without detailing all of the 



