476 



THE RESPIRATORY MECHANISM. 



the vagal supply? Loss of sensation points to inhibited func- 

 tion, and not to engorgement of the bronchial mucous mem- 

 brane. And yet we may have engorgement without functional 

 erethism, if it is due, not to the presence of blood fully charged 

 with oxygen, but to blood which, through the very fact of 

 being dammed up in the vascular channels, is reduced therein 

 to practically the condition of venous blood. The effusion of 

 mucus into the bronchi and pulmonary engorgement would 

 occur as normal consequences of such a state of things. But 

 how account for this vascular dilation without granting vaso- 

 motor attributes to the vagal plexuses? We might incriminate 

 sympathetic filaments were it not in the neck i.e., above the 

 spinal embranchments that the vagus was cut. But no error 

 is possible; section of the vagus alone gives rise to the phe- 

 nomena mentioned. It is the terminals of this nerve, there- 

 fore, that are alone in question, and the loss of the impulses 

 which they transmit to the subepithelial vessels is accountable 

 for their occurrence. 



Again, one of the results of section is "paralysis of the 

 bronchial muscles." Vasomotor nerves, even apart from our 

 own views, are recognized factors of the circulation of any tis- 

 sue. We have proof of vasodilation in the effusion and pul- 

 monary engorgement as a result of the vagal section. Now, 

 coupling this with the mass of evidence we have submitted 

 that vasoconstriction is the primary factor of functional ac- 

 tivity, how can we account for the paralysis of the bronchial 

 muscles without granting the vagus terminals vasoconstrictor 

 functions? Again, the fact that cutting of both nerves in the 

 neck gave rise to paralysis of these muscles points to another 

 suggestive feature, namely: that the vagus must incite and 

 govern the motor impulses to these muscles, besides presiding 

 over the functional variations of caliber of their vessels. If 

 we now add to these manifestations of efferent nervous activity 

 those of afferent activity suggested by the loss of sensation 

 over the bronchial mucous membrane, it seems clear that we 

 have in the vagal nerves referred to an autonomous supply espe- 

 cially devoted to the functions of the bronchial tubes and their 

 ramifications down to but not including the pulmonary lobule. 

 The importance of this fact asserts itself when we realize that 



