574 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



tion ; asphyxia causes broncho-constriction, but not after section of the pueu- 

 mogastric nerves; after section of both vagi it is impossible to cause reflex 

 broncho-constriction or broncho-dilatation ; the constriction of the bronchi 

 may be so great as to reduce their calibres to one-half or one-third, or even 

 more. The above results are very instructive, and show (1) That broncho- 

 constriction or broncho-dilatation can be obtained by stimulating the peripheral 

 end of the vagus, and that these changes occur in the bronchi of both lungs 

 when only one nerve is excited, thus proving that each nerve supplies both 

 kinds of fibres to both lungs ; (2) that the same results can be obtained by ex- 

 citation of the central end of the cut nerve, thus showing that the pneumogas- 

 trics contain both afferent constrictor and afferent dilator fibres ; (3) that reflex 

 broncho-constriction and broncho-dilatation cannot be produced after section 

 of the vagi, thus proving that all of the efferent fibres pass through the pneu- 

 mogastrics ; (4) that asphyxia and the inhalation of CO 2 cause broncho-con- 

 striction, but not after section of the vagi, thus indicating that under these 

 circumstances the effects on the bronchi are reflex ; (5) that certain poisons 

 affect one or the other of these two sets of fibres. 



The presence of efferent vaso-motor fibres in the vagi has been disproved by 

 the results of experiments by Bradford and Dean, 1 and others. These observers 

 have shown, however, that the vagi contain afferent pressor fibres, irritation of 

 which is followed by constriction qf the pulmonary vessels that may or may 

 not be accompanied by constriction of the systemic vessels, the efferent fibres 

 in this case reaching the lungs through the sympathetic nerves. 



The existence of trophic fibres is generally admitted. After section of one 

 pneumogastric nutritive changes immediately begin in the lung of the corre- 

 sponding side, which changes are manifest in the appearance of inflammation 

 in the middle and lower lobes. Section of both nerves is followed by inflam- 

 mation in the middle and lower lobes of both lungs. 



The vagi contain sensory fibres for the larynx, trachea, and lungs, after sec- 

 tion of which fibres there is an absolute loss of sensibility in these parts. 



It is probable that the vagi contain secretory fibres for the mucous glands. 



Thus we find that the pneumogastric nerves supply the lungs with (1) 

 afferent inspiratory and expiratory fibres; (2) afferent and efferent broncho- 

 constrictor and broncho-dilator fibres ; (3) afferent pressor fibres ; (4) general 

 sensory fibres; (5) trophic fibres; (6) and probably secretory fibres for the 

 mucous glands. 



The Sympathetic Nerves. The sympathetics supply trophic and efferent 

 vaso-motor fibres. The efferent vaso-motor fibres pass from the spinal cord in 

 the anterior roots of. the second to the seventh dorsal nerve, inclusive, to join 

 the sympathetics, thence through the first thoracic ganglia to the lungs. 



The Ganglia. Nothing is known of the functions of the ganglia. 

 1 Journal of Physiology, 1894, vol. 16, p. 70. 



