[MACLEOD] THE RESPIRATORY CENTRE 97 



2. The alveolar air was analysed for CO2 in two of the cats and 

 it shows a progressive decrease which was more or less in proportion 

 to the increase in ventilation. There is only one experiment in which 

 sufficiently numerous data were secured to determine the precise 

 relationship between rate of increase in ventilation and alveolar CO2. 

 In this experiment an increase in volume from 916 to 1130 cc. per 

 minute corresponds to a fall in percentage of alveolar CO2 from 4-5 

 to 3-1, giving 1-4 per cent increase in CO2 for 214 cc. increase in air 

 breathed. Later, an increase in ventilation from 1180 to 1720 cc. per 

 minute corresponds to a decrease in CO2 percentage from 2-8 to 1-6 

 giving 1 • 2 per cent decrease in CO2 for 540 cc. increase in air breathed. 

 These results indicate that the ventilation increases out of proportion 

 to the decrease in alveolar CO2. 



3. The carbonate content of the blood decreases markedly in all 

 the three cases (X, XVII and XXII) in which it was measured, but 

 there are not sufficient data to say whether this is dependent upon a 

 "blowing ofif" of CO2 through the lungs, an "acapnia" in Mosso's 

 sense, or is due to the appearance of fixed acids in the blood. It has 

 been observed by Cannon and others^ working on the problem of 

 surgical shock that the CO2 absorbing power of the venous blood in- 

 variably becomes lowered when there is a decided fall in the arterial 

 blood pressure. In a general way a similar relationship appears to 

 exist in our observations, but it is impossible to conclude from the data 

 available whether the two values bear any necessary relationship to 

 each other. 



4. The H-ion concentration of the arterial blood, measured in 

 four of the observations, before exitus becomes decidedly raised (Ph 

 7-0-7 -1). In two of the experiments (Nos. X and XXXI) the animal 

 was practically dead when the blood was collected, so that the low 

 Ph may not be of much significance. In the case of the other two ex- 

 periments (Nos. XXX and XXII), however, the specimens were col- 

 lected while the animal was still breathing and they indicate a very 

 decisive degree of acidosis. 



5. Lactic acid was measured in three of the animals and is found 

 to be markedly increased in two (XXII and XXXI) and about the 

 upper limit of the normal value in the third (XVII). This observa- 

 tion corresponds with those made on P^ and would indicate that the 

 primary cause for the lowering of the blood carbonates and for the 

 hypernœa is the development of unoxidised acid in the organism. 



6. The acid excretion by the urine is depressed in the least acute 

 of the experiments (XVII) in which also there is no decided increase 



1 Cannon, W.B., Journ. of the Amer. Med. Assn., 1918. 



