88 THE ROYAL SOCIETY OF CANADA 



Short of making actual comparisons of the tension of carbon 

 dioxide in arterial blood and alveolar air, the most satisfactory evidence 

 that the percentage composition of the alveolar samples collected by 

 the present method really corresponds to the tension of the gas in 

 arterial blood is supplied by the constancy of the results in successive 

 samples of air. This constancy can be seen in the figures given in 

 the tables accompanying this paper. 



The percentage of carbon dioxide in the arterial blood was de- 

 termined by the method of Barcroft and Haldane, using 0-5 cc. of 

 blood and an excess of weak ammonia water, so that the precipitate 

 which is formed when acid is added to dislodge the CO2 does not make 

 the solution so thick as to interfere with the evolution of the CO2. 

 The Ph of the arterial flow was measured by the method of Levy, 

 Rowntree and Marriott (Archiv. of Int. Med., 1915, XVI, 389), the 

 exact Ph of the phosphate solutions used for comparison being deter- 

 mined by the electro-metric method. 



The total acidity of the urine was computed by adding (1) the 

 titratable acidity (in cc. n/10 acid per 100 cc. urine), after shaking with 

 excess of neutral potassium oxalate, using phenolphthalein as indica- 

 tor, and (2) the ammonia, using the permutit method of Folin and 

 Bell (J. Biol. Chem. N.Y., 1917, XXIX, 329). 



The quantity of lactic acid in the blood was determined by the 

 modified von Fiirth method described elsewhere by the author (Mac- 

 leod and Hoover, Am. Journ. Physiol., 1916-17, XLII, 460). 



Consideration of Results 



The present communication concerns the results obtained on 

 cats which continued to breathe more or less normally for at least 

 two hours following the decerebration. According to the behaviour 

 of the breathing, as judged from the minute- volume of respired air, 

 these animals could be divided into two main groups; in the one, the 

 breathing either remained about constant or it slightly decreased, 

 whilst in the other it progressively increased. In several animals of 

 the first group the observation was terminated by bleeding to death, 

 but in those of the second group it was usually continued until the 

 animal died. 



The results of a typical experiment of the first group of animals 

 are given in Table I : 



