326 EXPERIMENTAL INVESTIGATION OF THE ACTION OF MEDICINES. 



may also contain both inspiratory and expiratory fibres. It has 

 already been mentioned, that the accelerating fibres of the 

 vagus in the lungs are probably irritated in pneumonia, but in 

 bronchitis the expiratory ones are chiefly irritated, and give 

 rise to the expiratory efforts in coughing, which serve to expel 

 any irritating substance in the bronchi. When these fibres are 

 exhausted, or the respiratory centre is feeble or irresponsive, 

 the mucus will remain, and consequently strychnia suggests 

 itself as an auxiliary in such cases. If the irritation depend 

 on something which cannot be removed by coughing, such as 

 miliary tubercle, we employ opium, chloral, &c., which lessen 

 the excitability of the respiratory centre. 



Moderate irritation of the superior laryngeal nerve renders 

 the respirations slower but deeper ; a stronger irritation pro- 

 longs expiration ; and a very strong one causes the respiration 

 to stop entirely in the state of expiration (Eosenthal, Athemhe- 

 wegungen, p. 244) until the increasing venosity of the blood 

 greatly stimulates the respiratory centre, and causes respiration 

 again to connnence. 



Irritation of the inferior laryngeal nerve (Burkart, Pfliiger's 

 Arch., vol. i, p. 107), and of the supramaxillary (Kratschmer, 

 Sitzunges-her. der Wien. Acad., Math.-Nat 01. 1870, vol. Ixii, 

 Abt. 2, p. 24), and nasal branches of the fifth nerve, acts in a 

 similar way to irritation of the superior laryngeal nerve, as 

 well as irritation of the cutaneous nerves generally, and 

 especially of those of the face and chest. (Schiff, Co7npL 

 Bend., 1861.) 



We have then to find out whether the alteration in respira- 

 tion produced by any drug is due to its action on the respiratory 

 centre, or on some of the nerves which influence it ; and the 

 following table may help us to do so more readily, by showing 

 at a glance the chief ways in which the respirations may be 

 accelerated or retarded. 



_r. • f r Excitement of / Increased irritation of the vagus. 



Ihe resp'.ratorj . nerves. \ By action of voluntary centre. 



movements J - f Increased temperature of blood. 



may be quick- ^. Greater excitement of 1 i^,,,,,,^ ^J^^^^ ^f ^lood. 



ened by I resp. centre. ^ ^^^.^^ ^^ ^^,^g^^ ^ 



