INNERVATION OF THE RESPIRATORY MOVEMENTS. 683 



extends in rabbits from a point 3 or 4 mms. in front of, to a point 

 2 or 3 mms. posterior to the calamus. No especial group of cells 

 can be found in this region sufficiently separated anatomically to 

 make it probable that they constitute the center in question. The 

 region has been delimited by vivisection experiments only, and, 

 according to Gierke, corresponds in location to the position of the 

 solitary bundle (tractus solitarius). According to Mislawsky,* 

 it lies near the mid-line in the formatio reticularis, while Gadf givet^ 

 it a relatively large area in the lateral portion of the formatio 

 reticularis, the continuation into the medulla of the lateral horn of 

 the gray matter of the cord. Destruction of these areas or section 

 of the cord anywhere between this region and the origin of the 

 phrenic nerve cuts off the respiratory movements, except those of 

 the nose and larynx, and causes death. The rapid death from 

 injuries to the cord or medulla in this region — from hanging, for 

 instance — is explained by the effect upon the respiratory center 

 or its connections. 



There is no doubt that the respiratory center in man occupies the same 

 general position as in the other mammals. There is on record a casef in 

 which sections were made of the medulla in a new-born infant. On delivery 

 it was necessary to puncture the cranium and remove the brain. The child 

 still lived and the medulla was cut across with scissors. A section at the 

 posterior end of the calamus stopped the respirations immediately, while 

 one somewhat anterior had failed to have this effect. 



The general idea of the connections of this center with the respir- 

 atory muscles may be described as follows: The respiratory fibers 

 arising in the center pass down the cord, probably in the antero- 

 lateral columns, and end in the gray matter of the cord at the 

 different levels at which the motor nuclei of the respiratory nerves 

 are situated. Whether the connection between the respiratory 

 center and the spinal motor nuclei is made by one or by a series of 

 neurons is not known, but we may assert that the nerve path 

 from the respiratory center to the respiratory muscles must be 

 composed of at least two neurons. According to this conception, 

 the impulses of inspiration and expiration for the entire respira- 

 tory mechanism originate in the medullary center and are thence 

 distributed in a co-ordinated way to the lower motor centers in 

 the cord, or, in the case of the nose and larynx, to the motor 

 centers of the vagus and facial. 



The Automatic Activity of the Respiratory Center.— The 

 constant activity of the respiratory center throughout life suggests 

 the question as to its automaticity. Is it automatic like the heart? 



* Mislawsky, "Centralblatt f. die med. Wissenschaften," No. 27, 1885. 



t Gad, "Archiv f. Physiologic," 1893, p. 75. 



X See Kehrer, "Monatshefte f. prakt. Dermatol.," 28, 450, 1892. 



