466 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



timi ; asphyxia causes broncho-constriction, but not alter section of the pneu- 

 mogastric oerves; 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. Theabove 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, tints 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 efferenl fibres pass through the pneu- 

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

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

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

 affect one or the other of these two sets of* fibre-. 



The presence of efimit r <i so- motor fibres in the vagi has been disproved by 

 die 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 of the pulmonary vessels that may or may 

 nor be accompanied by constriction of the systemic vessels, the efferent fibres 

 in this ease 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 lung.-. 



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

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



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



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

 afferent inspiratory and expiratory fibre.-; (2) afferent and efferent broncho- 

 constrictor and h'onclw-dilator fibre-; (3) afferent pressor fibres; (4) general 

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

 mucous glands. 



The Sympathetic Nerves.- — The sympathetics supply trophic and efferent 

 vaso-motor fibre-. The efferenl vaso-motor fil>res pass from the spinal cord in 

 the anterior root- of the second to tin- seventh dorsal nerve, inclusive, to join 

 the sympathetics, thence through the first thoracic ganglia to the lung-. 

 The Ganglia. — Nothing i- known of the functions of the ganglia. 



1 .fniirnnl i,f I'hii.-iohnfii. I S'.t |, vol. ]f>, p. 70. 



