NERVOUS MECHANISM OF RESPIRATION 167 



The respiratory center is in the lower part of the medulla 

 oblongata. Destruction of the encephalon above, or the cord 

 below, the center does not arrest respiration. It is bilateral a 

 center for each side and these are more or less independent of 

 each other, but are so intimately connected by commissural 

 fibers that any impression made upon one usually produces a 

 like effect upon the other. Each half presides over the lungs 

 and respiratory muscles of its own side, but acts synchronously 

 with its fellow of the opposite side. Furthermore, each of these 

 lateral centers may be regarded as consisting of two parts, one 

 for inspiration and one for expiration. Stimulation of the in- 

 spiratory center not only strengthens the inspiratory act, but 

 also accelerates respiration. Stimulation of the expiratory 

 center strengthens expiration and also retards the respiratory 

 rate. The accelerator portion of the center seems more sensi- 

 tive than the inhibitory, and the result of stimulation of the 

 whole center is therefore quickened respiration. 



Subsidiary respiratory centers are said to exist in the tuber 

 cinereum, optic thalamus, corpora quadrigemina, pons Varolii 

 and spinal cord; but the existence of at least some of these is 

 doubtful. 



Rhythm of Respiration. What agency excites the center to 

 keep up the respiratory movements with such regularity is a 

 matter of interest. The chief circumstances which seem to 

 affect the rate and rhythm are (i) the will, (2) emotions, (3) com- 

 position of the blood and (4) afferent impressions. 



i, 2. The effect of the will and emotions are too apparent 

 . to call for comment, i and 2 are properly included in 4. 



3. A deficiency of O or an excess of CO 2 in the blood will 

 increase the rate. Increase in temperature of the blood, as in 



ever, will produce a similar effect. 



4. The most important of these agencies is found in afferent 

 impressions conveyed to the center. The fibers carrying these 



mpressions are chiefly in the pneumo gastric, glosso-pharyngeal, 



