THE INDIVIDUAL GROUPS OF PROTEINS 489 



The process of estimation is carried out as follows : 



The water is saturated with coal gas by attaching the cap of the 

 special tube for the purpose to a gas burner and passing in the gas. 

 The water is shaken several times with the gas so that it becomes 

 saturated. 



In the small tube, which is graduated in percentages from o to 100 

 or 1 20, is placed less water than will be ultimately needed to dilute 

 the blood to the required tint. It contains 2 c.c. when filled up to the 

 mark 100. 



The finger is pricked with the lancet and blood is sucked up into 

 the capillary pipette a little beyond the mark 20 ( = 20 cmm. or 

 0*02 c.c.). The point of the capillary is wiped clean and the pipette 

 is dabbed on the back of the hand until the blood stands at the mark. 

 The blood is blown to the bottom of the tube below the water ; the 

 pipette is rinsed out with the water above it The solution is care- 

 fully diluted and mixed with water saturated with coal gas and its 

 tint is compared with that of the standard. Two readings should be 

 taken: (i) when the colours are the same, (2) when the colour is 

 appreciably lighter. The mean of these is taken. The scale gives 

 percentages of haemoglobin. 



(7) Saklfs Method. 



In principle and practice this method is the same as Gowers' or 

 Haldane's method, but the standard is a small tube of acid haematin. 

 20 cmm. of blood are put into 'iN hydrochloric acid in the com- 

 panion tube. Conversion to acid haematin takes place and the solu- 

 tion is diluted until it matches the standard. 



In many respects this method is preferable to the previous ones. 



B. By Determination of the Oxygen Capacity. 



The determination of the oxygen capacity of blood is described on p. 498. 



The amount of haemoglobin can be calculated from the following data : 



i c.c. of normal blood combines with -185 c.c. of O 2 at o and 760 mm. 



i gm. of haemoglobin combines with 1-34 c.c. of O 2 at o and 760 mm. 

 from which it is found that 



i c.c. normal blood contains '138 gm. of haemoglobin. 



Normal blood thus combines with 185 per cent, of oxygen at o and 

 7 60 mm. and contains 13-8 per cent, of haemoglobin. If the haemoglobin is ex- 

 pressed as 100, the oxygen capacity value must be multiplied by ^- or 5-4 



