LESSON XXIX 

 RESPIRATION (Continued) 



LOCALIZATION OF THE RESPIRATORY CENTER. PLACENTA. RESPIRA- 

 TION IN THE FISH 



1. The Localization of the Respiratory Center. Anesthetize a cat 

 and maintain the anesthesia until the animal has been killed. Perform 

 tracheotomy. Place the animal upon its ventral surface. Make a 

 median incision through the skin covering the region of the lower cer- 

 vical and upper thoracic vertebrae. Identify the spinous process of the 

 seventh cervical vertebra and follow this projection to the lamina?, re- 

 tracting the spinal muscles. Stop bleeding by applying dry tampons 

 or by torsion and ligation of the blood-vessels. Cut away the laminae 

 and process of the seventh vertebra until a short segment of the spinal 

 cord has been exposed. With a curved needle draw a loose ligature 

 around the cord. 



Apply a stethograph to the chest of the animal and allow the record- 

 ing drum to register the respiratory movements upon a slowly revolving 

 kymograph. A sufficiently long normal record having been obtained, 

 raise the spinal cord and divide it. The animal continues to respire 

 normally, showing thereby that this lesion does not interfere with the 

 efferent impulses to the muscles of respiration. Divide the students 

 into three groups, and proceed as follows: 



Group A. Expose the spinal cord in the region of the third cervical 

 vertebra. Place a loose ligature around it, and divide it after a short 

 normal tracing has been taken. The respiratory movements cease 

 almost immediately, owing to the fact that the transection has separated 

 the nuclei of the respiratory nerves, principally those of the phrenic 

 nerves, from the respiratory center. The latter, therefore, must lie 

 above this section. 



Group B. Make a median incision through the skin covering the 

 occiput. Advance in the direction of the foramen magnum. Enlarge 

 the opening until a clear view of the region of the pons is obtained. 

 Divide the latter structure transversely above the medulla oblongata. 

 Since the animal continues to breathe, the principal center of respiration 

 must be situated below this level. 



Group C. Make a median incision through the skin covering the 

 occiput. Palpate this region until a depression in the vertebral column 

 is clearly felt through which it is possible to reach the medulla directly. 

 Pierce this structure with a pointed instrument. Respiration ceases 

 immediately. 



Compile the results of the three groups of students and draw con- 

 clusions regarding the location of the respiratory center. 



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