[MACLEOD] THE RESPIRATORY CENTRE 99 



We have preserved the anterior portions of the heads of numerous 

 animals in subsequent experiments of a similar type, and we hope in 

 the near future to be able to furnish data which will enable us to state 

 precisely where the cut should be situated for satisfactory breathing. 

 As far as we can say at present when the posterior corpora quadrige- 

 mina are even slightly wounded spontaneous respiration is seldom, if 

 ever, observed. 



In collaboration with Lois Fraser and R. S. Lang, I have found, 

 however, that perfectly regular respirations may reappear in animals 

 of the above type by greatly raising the partial pressure of oxygen in 

 the alveolar air. This is done by passing a catheter into the trachea so 

 that its open end lies above the bifurcation, and then discharging 

 washed oxygen at a rapid rate from a cylinder of the gas. In a few 

 minutes, during which artificial respiration may be necessary in order 

 to carry the oxygen to the alveoli, the animal usually begins to breathe 

 in perfectly normal fashion and continues doing so for hours. We are 

 at present engaged in studying the very interesting and far-reaching 

 problems which this observation presents; for the present we may 

 point to the interesting evidence it affords that oxygen deficiency, 

 per se, far from acting as a stimulus for the respiratory centre, renders 

 it incapable of rhythmic function, at least in conditions where it is 

 imperfectly supplied with blood, as after decerebration. In this con- 

 nection attention should again be called to the fact that if the breath- 

 ing of the decerebrate animal becomes feeble during compression of the 

 vertebral arteries, it can be restored to normal by releasing the blood 

 flow. 



Conclusions 



After removal of the cerebral hemispheres a certain number of 

 cats continue to breathe in perfectly normal fashion for several hours; 

 others fail to respire adequately and still others breathe normally 

 for some time, but subsequently become hyperpnoeic, and finally are 

 usually seized by convulsions to which they succumb. These differ- 

 ences in behaviour seem to be dependent upon the age of the animal 

 and the level at which the section of the mesencephalon is made. 

 Spontaneous breathing is decidedly more likely to return in the 

 younger animals and when the cut is not further back than the an- 

 terior edge of the anterior corpora quadrigemina. When the cut is 

 further forward the decerebrate animal is hyperexcitable, decerebrate 

 rigidity is marked, and the animal usually becomes hyperpnoeic. 

 When the cut is farther back, adequate spontaneous breathing is un- 

 usual. 



