162 SECTIONAL ADDRESSES. 



tEafc in the veins. It is possible to calculate, as indeed has been done 

 by my colleague, Mr. Eoughton, what the amount of oxygen leaving 

 the capillaries is. The answer is not "059, as in the case of the normal, 

 but '026 — less than half the normal. So, other things being equal, 

 cutting down the oxygen pressure in the arterial blood to 31 and the 

 percentage saturation to 66 would deprive the tissues of half their 

 oxygen. With this compare an example of the anaemic type. The 

 arterial blood shall have the same total quantity of oxygen as in the 

 anoxic case, but instead of being 66 per cent, saturated it shall contain 

 66 per cent, of the total haemoglobin, which shall be normally satm-ated. 

 The amount of oxygen which would pass to the tissues under these 

 conditions is '041 c.c. — more than half as much again as from the 

 anoxic blood laden with the same quantity of oxygen. 



And thirdly, let us take for comparison a case of stagnant anoxaemia 

 in which the same quantity of oxygen goes to the tissue in the cubic 

 centimetre of blood as in the anoxic and anaemic types. On the assump- 

 tion which we have made the quantity of oxygen which would lea^TQ 

 the blood would be '045 c.c. » 



In round numbers therefore the prejudice to the tissues may be 

 expressed by the following comparison. In this case both of the 

 oxygen going to the blood and going into the tissues I have called the 

 normal 100. This does not, of course, mean that the two amounts are 

 the same. The former in absolute units is about three times the latter. 

 The figure 100 at the top of each column is merely a standard with 

 which to compare the figures beneath it. 



Oxygen in 1)100(1 going Oxygen leaving the blood 



to vessels of tissue. to supply the tissues. 



Per cent. Per cent. 



Normal .... 100 100 



("Anoxic . . 66 42 



Anoxaemia \ Anaemic . . 6fi 66 



I Stagnant . . 66 75 



Measure7nent of Anoxminia. 



In the study of all physical processes there comes a point, and that 

 very early, when it becomes necessary to compare them one with 

 another, to establish some sort of numerical standard and have some 

 sort of quantitative measurements. The study of anoxaemia has reached 

 that point. By what scale are we to measure oxygen want ? 



Let us take the anoxic type first. There are two scales which 

 might be applied to it, both concern the arterial blood; the one is the 

 oxygen pressure in it, the other is the actual percentage of the haemo- 

 globin which is oxyhaemoglobin. A third possibility suggests itself, 

 namely, the actual amount of oxygen present, but this would be in- 

 fluenced as much by the anaemic as by the anoxic conditions. Of the 

 two possibilities — that of measuring the pressure, and that of measuring 

 the saturation of the blood with oxygen — the latter is the one which is 

 likely to come into vogue, because it is susceptible of direct measurement. 



Two convei'ging lines of work have within the last few years brought 

 us nearer to being able to state the degree of anoxaemia in man in terms 

 of the percentage saturation of oxygen in his blood. The first,. inti'O- 



