CENTRAL AUTONOMIC MECHANISMS 



959 



nerves was also shown. The afferent and efferent 

 paths for the various circulatory reflexes are presented 

 in detail by (Jvnas in Chapter XLI\' of this volume. 



CONTROL OF RESPIRATION AND ALLIED FUNCTIONS. In 



igi6 Miller & Sherrinoton {115) also explored the 

 floor of the fourth ventricle with electrical stimula- 

 tion in decerebrate cats and found that stimulation of 

 a v-ery restricted area of the inferior fovea produced 

 swallowing (fig. 4). There was concurrent arrest of 

 respiratory movements and also increased pulse rate. 

 These phenomena were also shown to occur in normal 

 swallowing. In other early experiments Graham 

 Brown (65) stimulated the surface of the transected 

 brain stem of a chimpanzee and from the region of 

 the central gray obtained an increased respiratory 

 rate and a sound which resembled laughter. It re- 

 mained for Pitts and his collaborators, however, to 

 explore thoroughly the respiratory mechanisms of the 

 lower brain stem (136). The medullary respiratory 

 center has been found to have two parts bilaterally 

 located. The first, for inspiration, is located in the 

 ventral reticular formation immediateh' overlving 

 the rostral four fifths of the inferior olive and extendina; 



a few millimeters to each side of the mid-line. In- 

 crease in the carbon dioxide content of bod\- fluids 

 causes increase in the frequency of discharge and re- 

 cruitment of neurons in this center and, as a conse- 

 quence, increase of the depth of inspiration. The 

 center for expiration is located in the dorsal reticular 

 formation, dorsal and slightly rostral to and cupped 

 o\er the end of the inspiratory area. It acts, in part 

 at least, by inhibiting the inspiratory center. Upon 

 these centrally located mechanisms varying types of 

 afferent impulses converge from the skin, the nose, the 

 bronchi, the lungs, etc. Chemical changes in the 

 blood and accumulation of metabolites affect the 

 cells of these centers directly; they also stimulate 

 peripheral chemoreceptors which send afferent im- 

 pulses into the respiratory mechanisms. Since nervous 

 control of respiration will be thoroughly discussed in 

 Chapter XLIII of this volume by Oberholzer & 

 Tofani, a detailed discussion is not in order here. 

 Briefly, the regulation of rh\ thmic respiration appears 

 to depend upon the alternating activity of the two 

 portions of the respiratory center. This activity de- 

 pends upon several factors, of which one is a vagal 

 reflex system sensitive to stretch of the lungs; another 



Tr&c t JOlittLT. 



FIG. 4. Cardiac and respiratory changes 

 associated with swallowing induced by 

 stimulation of the floor of the fourth ven- 

 tricle in the decerebrate cat. The point of 

 application of the stigmatic electrode is 

 sliown. [From Miller & Sherrington (115).] 



