366 PHYSIOLOGY. 



has two functionally symmetrical halves, one on each side of the 

 median raphe. If separated by means of a longitudinal incision, the 

 respiratory movements continue symmetrically on both sides. De- 

 struction of one-half of the medulla is attended with paralysis of 

 respiration only on that side, seeming to prove that each half of the 

 center is particularly concerned in the respiratory muscles of its 

 own side. 



During ordinary breathing impulses are sent from the respira- 

 tory center down the antero-lateral columns of the spinal cord to the 

 cells of the anterior horns, then along the phrenics to the diaphragm 

 and along the intercostal nerves to those muscles which elevate the ribs. 



ACTION OF BRAIN IN FRONT OF THE RESPIRATION-CENTER. If the 

 tracts from the brain to the center of respiration with the vagi are 

 divided, there ensues a want of rhythm in the respiratory movements. 

 Here we have two afferent tracts removed, one in front, from the brain, 

 the other by the vagi. Martin and Booker found that irritation of the 

 mid-brain increased the number of the respirations and produced 

 inspiratory arrest. Lewandowsky holds that the posterior corpora 

 quadrigemina have a center which actively inhibits the center of 

 inspiration. 



While it seems to be undisputed that the principal respiratory 

 center lies in the medulla and that upon it depends the rhythm of 

 the respiratory movements, yet there have been found other supposed 

 subordinate centers located in the cord. These, however, do not 

 exist. 



The cutaneous nerves also exercise some effect upon respiration. 

 The most marked influence is exerted by those of the face (trigem- 

 inus), abdomen, and chest. Both thermal and mechanical stimuli 

 easily excite them. 



Irritation of the trigeminus by surgical operation, as in the 

 removal of the adenoids, has been shown by Drs. W. H. Good and 

 Harland to inhibit the respiratory movements and the cardiac action. 

 Hering has shown that inflation of the lungs causes a marked 

 increase in the number of heart-beats. He believes that the sen- 

 sory nerves of the lungs stand in the same relation to the cardio- 

 inhibitory center as the nervous depressor does to the vasomotor 

 center. That is, irritation of the sensory terminals in the lungs, by 

 inflation, causes reflexly a loss of tonus in the cardio-inhibitory cen- 

 ter and a resulting increment of heart-beats. Dr. Jackson, in a case 

 of inhibition of the heart and of respiration from trigeminal irrita- 

 tion, resuscitated a patient by mouth-to-mouth inflation. Dr. W. H. 



