A topical synopsis of lectures on animal physiology / by Henry Sewall.

  • Sewall, Henry, 1855-1936.
Date:
1888
Catalogue details

Licence: Public Domain Mark

Credit: A topical synopsis of lectures on animal physiology / by Henry Sewall. Source: Wellcome Collection.

Provider: This material has been provided by the Augustus C. Long Health Sciences Library at Columbia University and Columbia University Libraries/Information Services, through the Medical Heritage Library. The original may be consulted at the the Augustus C. Long Health Sciences Library at Columbia University and Columbia University.

    127/284 (page 121)
    —63— atory movements of the mouth parts, though these are ineffi- cient to aerate the blood. When the vagi are divided on each side of the neck the respiratory movements become slower and deeper, but do not cease. When the central end of the cut vagus is gently stimulated the respiration is quickened, and it may be so hastened that the respirations are fused together and the muscles come to a tetanic standstill in the phase of inspiration. When the central end of a superior laryngeal nerve is stimulated the respiration because slower and deeper, and if the stimulus be sufficiently strong expiratory tetanus is pro- duced. The same is true, but to a slighter extent, of the inferior laryngeal nerve. It is not improbable that the mere mechanical conditions of the lung in the phases of expiration and inspiration excite the respective movements of inspiration and expiration. It is clear, then, that the respiratory centre is under the modifying control of stimuli proceeding to it along afferent nerves; but that the essential activity of the centre is quite in- dependent of any stimulus reaching it from without. THE EXCITING CAUSE OF THE RESPIRATORY MOVEMENT. The action of the respiratory centre is determined by the condition of the blood supplying it. The centre is made active by venous blood, but is not ex- cited by arterial blood. It appears to be the want of oxygen and not the excess of carbonic acid which stimulates the centre, as shown by the re- spiratory disturbance of an animal breathing in an atmosphere of hydrogen. The activity of the respiratory centre is determined by the direct influence of the blood upon it, irrespective of the condi- tion of the blood in other parts of the body. We may suppose that the activity of the respiratory centre causes an accumulation of stimulating waste products in it,