ii2 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



respiratory activity of the gills in fish are situated in 

 the medulla. Could it not be possible that in Mam- 

 malians the segmental ganglia for the gill-respiration 

 continue to be active, although the gills or the oral 

 respiration have disappeared ? If this were so, we can 

 understand that the segmental ganglia for gill-respi- 

 ration in the medulla begin to be active first. Their 

 activity is the stimulus for the activity of the next 

 lower segmental ganglion, and so on. 



If we cut the cord between medulla and phrenic 

 nerve, respiration must stop. But if we could keep 

 such an animal alive lonof enough, the lower seamen- 



o o o 



tal ganglia would be altered in such a way as to 

 breathe automatically again. 



That the shock-effect after such an operation can- 

 not be due to an exhaustion of the phrenic ganglia is 

 made obvious by the following experiment : W. T. 

 Porter made hemisections of the spinal cord between 

 the medulla oblongata and the origin of the phrenic 

 nerves (3). If one half, for instance the left half, of 

 the medulla be cut, the left half of the diaphragm no 

 longer partakes in the respiratory movements, while 

 the respiratory motions of the right half continue. 

 But if the right phrenic be cut, the left half of the 

 diaphragm begins its rhythmical motion again, while 

 the right half of the diaphragm stops breathing. It 

 is of course, at present, just as impossible to explain 

 why the cutting of the right phrenic nerve causes the 

 left half of the diaphragm to breathe again, as it is to 

 explain why a frog that had lost its spontaneity after 



