OTHER SENSORY NERVES. 305 



therefore a series of small elevations rising from the base line correspond- 

 ing to the condition of relaxation. 



Inferior laryngeal nerve. — Excitation of this nerve is frequently 

 attended by inhibition of inspiration, with sometimes active expiratory 

 movements. 



Glosso-pharyngeal nerve — Kronecker and Meltzer, 1 in studying the 

 mechanism of deglutition, found that the small inspiration mentioned 

 above, which accompauies the first phase of this act, is followed by a 

 period during which respiration is entirely inhibited. This result they 

 ascribed to an irradiation from the centre of deglutition to the respira- 

 tory centre. Marckwald 2 has shown, however, that the pause is 

 originated reflexly by means of the glosso-pharyngeal nerve. If this 

 nerve be cut and its central end stimulated, after a latent period of half 

 to one second, an absolute stoppage of respiration takes place. This 

 stoppage differs from that produced by any other nerve, in that the 

 muscles remain in the condition in which they were when the stimula- 

 tion began to act, whether during inspiration, expiration, or midway 

 between the two conditions. This cessation of respiration lasts for 

 about the time occupied by the two or three preceding respirations. 

 Eespiration then recommences, even though stimulation be continued, 

 with an inspiration which starts from the position at which the 

 diaphragm was arrested at the beginning of stimulation. 



Other sensory nerves — Gentle stimulation of most sensory nerves 

 causes quickening and increase in the inspiratory movements ; with a 

 stimulation strong enough to evoke signs of pain, the animal becomes 

 restless, and the breathing is mainly of the active expiratory type. The 

 application of gentle stimuli to the stomach or abdominal viscera, or to 

 the splanchnic nerves, is, however, invariably expiratory, and displays 

 itself either as an increase in the expiratory pauses, or more often as a 

 strong contraction of the expiratory muscles. 



A pure expiratory reflex may also be brought about by gentle 

 stimulation of the nasal mucous membrane of the rabbit, as by applica- 

 tion of chloroform vapour. A similar expiratory pause is caused in 

 many animals by dipping the nose into water, or even by plunging the 

 lower half of the body into water {Tauchreflex). The temperature of 

 the water is of no influence on the results of the experiment. Fredericq 3 

 has shown that a specially long expiratory pause may be produced in a 

 diving animal, such as the duck, by allowing a stream of water to flow 

 on its beak. The teleological importance of these reflex cessations of 

 respiration, which have been classed together by Miescher-Busch 4 as 

 apnoea spuria, is obvious. 



Influence of the higher parts of the brain on the respiratory 

 centre. — We have seen that a complete section of the bulb above the 

 respiratory centre is without influence on the respiratory rate, the 

 centre with the help of the vagi being quite sufficient to carry out the 

 normal respiratory rhythm. If, however, the vagi have been previously 

 divided, the severance of the paths from the higher parts of the brain 

 has an enormous influence. The previous rhythmic respiratory move- 

 ments are practically abolished, and give place to a series of prolonged 

 inspiratory spasms, which are separated by long pauses during which 



1 Arch./. Physiol., Leipzig, 1888, Suppl. 



2 "Movements of Respiration, " 1888, p. 88. 



3 Arch. f. Physiol., Leipzig, 1893, Suppl., S. 65. 4 Ibid., 1885, S. 355. 



VOL. II. — 20 



