86 THE ROYAL SOCIETY OF CANADA 



normal as in an anaesthetised animal with brain intact. It is clear, 

 however, that important facts are likely to be revealed by observing 

 the behaviour of the decerebrated animal in relationship to changes in 

 the chemical condition of the arterial blood, an investigation which is 

 very difficult in man, and which can be carried out in anaesthetised 

 animals only to a limited degree because of the presence of anaesthetics 

 in the blood. 



It has been noted by several of the above-mentioned workers, 

 particularly by Theile (loc. cit.) and Weed (Weed, L. H., Am. Journ. 

 Physiol., 1917, XLIII, 131.) that the character of the respirations does 

 not remain the same throughout the period during which the animal 

 survives thé decerebration. Weed recognizes three periods of some- 

 what different behaviour of the decerebrated animals; in the third of 

 these, which supervenes in from two and one-half to three hours 

 following the decerebration, increasing respiratory difficulties with 

 rapid decline are often observed. 



In a series of investigations, conducted in the author's labor- 

 atory by R. W. Scott, in which the particular problem was to study 

 the influence of rapidly increasing percentages of carbon dioxide in 

 the inspired air and of intravenous injections of alkali on the respira- 

 tion of decerebrate cats (Scott, R. W., Am. Journ. Physiol., 1917, 

 Vol. 44, 196), it was noted that there were three more or less distinct 

 groups of animals. In one of these, adequate spontaneous respiration 

 did not return, or if it did so it was irregular and incapable to main- 

 tain life. In a second group the breathing was fairly satisfactory 

 for the first hour or so but then became dyspnoeic and gasping, and the 

 animal soon succumbed. In the third group the animal breathed 

 with perfect regularity for many hours, and even at the end did not 

 develop the dyspnoea characteristic of the second group. 



Since these variations might lead to serious confusion in the fur- 

 ther researches which were contemplated, it was decided to make a 

 closer study of the breathing and particularly to see whether varia- 

 tions in it are correlated with changes in the acid-base equilibrium of 

 the blood. It is with this phase of the problem that the present paper 

 is concerned. 



Methods 



Decerebration was performed with the apparatus and by the 

 method described by Miller and Sherrington (Quart. Journ. Physiol., 

 1915, IX, 107). It is of interest to note that frequently the respira- 

 tions became regular almost immediately after the decerebration and 



