430 Dr. F. Semon. On the Position of the 



speak very clearly of the necessity of the existence of a similar 

 arrangement. The full physiological importance of it, however, 

 appears to have only comparatively recently occurred to Krause and 

 to myself, independently of one another, and to have been brought 

 forward equally independently and simultaneously at the Inter- 

 national Congress of 1884, as stated at the beginning of this 

 paper. 



The existence of such a tonus fully explains the difference between 

 the conditions of the glottis as seen during quiet respiration and after 

 death, and explains also why the interposition of the phonatory 

 apparatus in the air passages has not been followed by any change in 

 the type of normal respiration in man. In virtue of their preventing 

 such a change, i.e., of either increased labour on the part of the 

 regular muscles of respiration or of the accessory muscles of respira- 

 tion having to work constantly even during quiet respiration, the 

 glottis openers, i.e., the posterior crico-arytenoid muscles, appear to 

 me to deserve undoubtedly a much higher position in the mechanism of 

 respiration than has been so far accorded to them. 



The only remaining question then would be : is this tonus of the 

 abductor muscles an automatic one ? i.e., is it induced in the respira- 

 tory centre itself, or is it of the nature of a reflex tonus, i.e., only 

 engendered in the respiratory centre through peripheral influences H 



Athough it has been shown by Rosenthal that the respiratory 

 centre in the medulla oblongata, even after the section of both pneu- 

 mogastric nerves, and after removal of the cerebrum as well as after 

 section of the cervical part of the spinal cord, is capable of engender- 

 ing rhythmic movements (so that its action in a certain sense must 

 certainly be looked upon as an automatic one), yet at the same time 

 there can be no doubt as to the existence of afferent impulses com- 

 municated to it along the most various peripheral nerves, and most 

 of all along the main trunk of the pneumogastric. Whilst therefore, 

 a priori, it would not at all be impossible that the tonus of the 

 abductors of the vocal cords might originate in the respiratory centre 

 itself, it seemed, in concord with general experiences concerning the 

 nervous mechanism of respiration, at least equally probable, that 

 impulses might be conducted rhythmically along the afferent fibres of 

 the pneumogastric nerves to the respiratory centre, and there be 

 changed into a tonic setni-innervation of the posterior crico-arytenoid 

 muscles, which again under the influence of any of the extraneous 

 causes above mentioned could be changed into rhythmical impulses 

 coincident with and renewed with every respiratory movement. 



It occurred to me that a more definite solution of this question 

 might be hoped for, if it were possible to cut both pneumogastric 

 nerves below the points from which the recurrent laryngeal nerves 

 are given off. One could not hope that this experiment would deti- 



