542 



VETERINARY PHYSIOLOGY 



and, after equilibrium has been established, is withdrawn and 

 analysed. Its volume is measured in a fine graduated tube. 



It is then forced through 

 caustic soda solution till 

 all the CO2 is absorbed, 

 again drawn into the 

 tube and measured, the 

 decrease in volume giv- 

 ing the amount of CO,. 

 Next, it is passed through 

 a solution of sodium 

 pyrogallate in caustic 

 soda to absorb the Og 

 and is aoain measured. 

 ^ ^ The residual gas is nitro- 



FiG. 220.-Krogh's Microtonometer. B., g^l^, a _ small amount of 

 chamber attached to blood-vessel whicll is always dissolved 

 with bubble of air ;•!., fine graduated -^^ ^y^^ ^^^^^^ p^om the 

 tube in water jacket tor analysis of 



gases. " percentage of these gases 



in the bubble their ten- 

 sion in the circulating blood in which the bubble of air lay 

 is calculated. The apparatus is shown in fig. 220. 



It has been found that the tension of COo in arterial blood 

 is identical with that in the air in the vesicles of the lungs. 

 When the amount in the air is altered, the tension in the blood 

 follows the variation. 



The O2 tension in venous blood is in all cases lower (by 1 to 

 4 per cent.) than that in the air of the lung vesicles, and it also 

 follows any alteration in the latter. 



Krogh has also shown that, by modifying the air breathed, 

 Oo may be made to come off from the blood, and COo to 

 be taken up by the blood. 



The difference in the pressure of these gases in the alveolar 

 air and in the blood may be represented as follows in mm. Hg : — 



Oxygen. 



Carbon Dioxide. 



Alveolar Air . 

 Blood from Lungs 



42 

 42 



