THE NERVOUS REGULATION OF RESPIRATION 529 



others have shown that it is possible to make a median incision through 

 this structure without destroying the respiratory movements. For this 

 reason, the center is said to be bilateral, each half being especially 

 concerned with the muscles situated on the corresponding side of the 

 thorax. In this connection brief reference should also be made to the 

 fact that injuries to the cerebral cortex (hemiplegia) most generally 

 leave the respiratory musculature unaffected. This is especially true 

 of the diaphragm and the intercostals. It seems, therefore, that these 

 muscles, besides being governed by lower centers, possess a bilat- 

 eral representation in the motor cortex of the cerebrum. Conse- 

 quently, the destruction of one motor area cannot possibly produce 

 a paralysis of the respiratory muscles, although it gives rise to a uni- 

 lateral paralysis of the other skeletal muscles. 



It might also be stated that several authors have not felt inclined 

 to accept this rather sharp localization of Flourens. Gierke, l for ex- 

 ample, regards the tractus solitarius as an important part of this cen- 

 ter, while Mislawsky 2 holds a similar view regarding a stretch of gray 

 matter in the vicinity of the hypoglossal nucleus. To be brief, it 

 seems that the respiratory center is not confined to a point-like zone 

 of bulbar gray matter, but occupies a more extensive area, inclusive of 

 its connections with other bulbar centers and the nuclei of important 

 cranial nerves. With Gad, 3 it may be assumed that really the entire 

 formatio reticularis enters into the formation of the bilaterally coordi- 

 nated center of respiration. 



A very general localization of this center may be effected in the 

 following way: A deeply anesthetized animal is connected with a 

 stethographic arrangement for recording the respiratory movements. 

 A section is then made transversely through the region of the pons. 

 Inasmuch as the respiratory motions continue after this cut has been 

 made, it is evident that the center is situated in the bulb or spinal 

 cord. A second cross-section is then made below the lower root of the 

 phrenic nerve, at about the level of the sixth cervical vertebra. Since 

 the respiratory movements do not cease even now, it is obvious that 

 the main center is situated above the level of the second cut, i.e., either 

 in the medulla or upper cervical cord. The latter point may now be 

 decided by piercing the lower region of the bulb, when the respiratory 

 motions will cease immediately. 



This result may also be obtained by dividing the spinal cord be- 

 tween the main center and the nuclei of the phrenic nerves situated 

 opposite the fourth and fifth cervical vertebrae. In this case, however, 

 the respiratory standstill is not caused by the destruction of the 

 center, but solely on account of its separation from its principal motor 

 apparatus, consisting of the phrenic nuclei and phrenic nerves innervat- 

 ing the diaphragm. Inasmuch as this muscle is absolutely essential 



1 Archiv fur Anat. und Physiol., 1893, 583. 



2 Zentralbl. fur die med. Wissensch., 1885, 465. 



3 Archiv fur Anat. und Physiol., 1893, 75. 

 34 



