136 HEMOGLOBIN 



myself — but I hope not the reader — by setting forth the principles 

 which underlie it. The reader can, and I hope will, refer to Hartridge 

 and Roughton's original papers for more detailed knowledge (4), 



Two solutions, I and II, the former of reduced haemoglobin, the latter 

 of oxygenated water, are prepared. Solution I contains haemoglobin 

 in about one-fortieth of the concentration in which it is present in 

 blood. Solution II contains the minimal quantity of oxygen necessary 

 for the reaction, thus making it as slow as possible. These solutions 

 are driven along rubber tubing and meet in a special apparatus. This 

 apparatus consists of a glass tube, at one end of which — that at which 

 they enter — there is a contrivance for mixing the fluids. The fluids 

 there are brought instantly into intimate contact after which they 

 traverse a glass tube. If the flow along the tube is sufiiciently rapid, 

 about 600 cm. per second, it is possible to detect a change of colour 

 in the first few centimetres. At first the fluid is appreciably " venous " 

 in coloiu": it rapidly becomes "arterial." It is possible to examine, 

 spectroscopically, the fluid at various fixed points in this zone of 

 changing colour and thus to determine the relative quantities of oxy- 

 and reduced haemoglobin at each station. Knowing the velocity at 

 which the fluid is running, the rate at which it changes from being 

 a mixture of reduced haemoglobin and oxygen to being a compound 

 of the two can be calculated. 



It is necessary to be certain that the time thus measured is actually 

 taken up by the act of chemical combination, and not merely by 

 the complete mixing of the oxygen solution with that of the haemo- 

 globin. Hartridge and Rough ton (4) made sure of their ground in this 

 respect in the following way. The solutions I and II were replaced 

 by an alkafine solution which contained phenol -phthalein and an acid 

 solution respectively. The strengths of acid and alkaU were such that 

 the mixed fluid would be just acid and therefore the indicator would 

 be bleached. Before the red colour could disappear completely three 

 things then must have happened: (1) the complete mixture of the 

 solutions, (2) the chemical action between the alkah and the acid, 

 (3) the reaction between the excess of acid (very dilute) and the 

 phenol-phthalein. Clearly the time which these three processes jointly 

 would require would exceed that occupied by the first — the mere 

 mixing. Yet the mixing was so rapid and so intimate that no red 

 colour could be detected beyond the first few millimetres of the tube. 



The second experimental precaution to which I shall allude is one 

 which ensures that at any particular spot the fluid over the whole 



