20 BLOOD 



It will therefore be seen that the blood has the power 

 of carrying a varying amount of acid with practically no 

 change in the H-ion concentration, and that this power 

 depends almost entirely upon the buffer action of NaHCOg. 

 We see further that the blood possesses a store of NaHCOa, 

 a store fluctuating in amount. Sodium bicarbonate is 

 therefore termed the alkaline reserve. It serves the purpose 

 of stabilising the H-ion concentration. When a more 

 stable acid such as lactic appears in the blood, it com- 

 bines with sodium and therefore reduces the amount of 

 NaHCOg. In small amounts this causes only a very slight 

 change in the H-ion concentration, but by reducing the 

 alkaline reserve it brings the blood nearer the margin of 

 stability. Such a condition of reduced alkaline reserve 

 is called acidosis. The blood can therefore be in a state 

 of acidosis without any appreciable rise in its H-ion concen- 

 tration. As the lactic acid is oxidised the alkahne reserve 

 is restored. 



Determination of the Allcaline Reserve : Van Slyl<e's Method 



Blood is collected under a layer of paraffin and centrifuged. 

 The plasma is removed and exposed to a sample of alveolar air. 

 A known volume is then treated with excess of 5 per cent. H2SO4, 

 frothing being prevented by addition of a drop of caprylic alcohol. 

 It is then put under reduced pressure and the CO2 driven off is 

 measured. Since this is the CO, combined chemically in the plasma, 

 the amount of NaHCO;; can be calculated. 



Determination of H-ion Concentration 



Electrical Method. 



Sorensen^s Method. — The plasma is treated with an indicator, 

 e. g. neutral red, and the colour matched with a series of phosphate 

 solution. 



Barcroffs Method. — This depends upon the fact that H-ion 

 concentration determines the form of the dissociation curve of 

 oxyhsemoglobin (p. 101). 



THE TOTAL AMOUNT OF BLOOD IN THE BODY 



This is estimated by two methods. 



