164 SECTIONAL ADDRESSES. 



the fact tHat it is the quantity of reduced hsemoglobin that is the index 

 of the anoxic condition. They speak not of the percentage saturation, 

 but of the percentage of unsaturation. A blood which would ordinarily 

 be called 85 per cent, saturated they speak of as 15 per cent, unsaturated. 



Anoxic anoxaemia, in many cases of lung affection, should be 

 measured by the direct method of arterial puncture, for the simple 

 reason that the relation between the alveolar air and the arterial blood 

 is quite unknown. Such, for instance, are cases of many lung lesions 

 of pneumonia in which the lung may be functioning only in parts, of 

 pneumothorax, of pleural effusions, of emphysema, of multiple pul- 

 monary embolism, in phases of which the arterial blood has been found 

 experimentally to be unsaturated. In addition to these definite lung 

 lesions, there is another type of case on which gi'eat stress has been 

 laid by Haldane, Meakins, and Priestley, namely, cases of shallow 

 respiration.' A thorough investigation of the arterial blood in such 

 cases is urgently necessary. Indeed, in all cases in which it is prac- 

 ticable, the method of arterial puncture is desirable. But in the cases 

 of many normal persons—as, for instance, those airmen at different 

 altitudes — alveolar-air determinations would give a useful index. 



The ansemic type of anoxaemia is gauged by the quantity of oxy- 

 haemoglobin in the blood. In the case of simple anaemias this is 

 measured by the scale in which the normal man counts as 100 and the 

 haemoglobin in the anaemic individual is expressed as a percentage of 

 this. This method has been standardised carefully by Haldane, and we 

 now know that the man who shows 100 on the scale has an oxygen 

 capacity of "185 c.c. of oxygen for every c.c. of blood. ^Ye can therefore, 

 in cases of carboxyhaemoglobin, or methaemoglobin poisoning, express 

 the absolute amount of oxyhaemoglobin pressure either by stating the 

 oxygen capacity and so getting an absolute measurement, or in relative 

 units by dividing one hundred times the oxygen capacity by •185, and 

 thus getting a figure on the ordinary haemoglobin metre scale. 



The MecJianisiii of Anoxtsmia. 



Perhaps the most difficult phase of the discussion is that of how 

 anoxaemia produces its baneful results. In approaching this part of 

 the subject I should like to warn my readers of one general principle 

 the neglect of which seems to be responsible for a vast dissipation of 

 energy. Before you discuss v,'hether a certain effect is due to cause A or 

 cause B, be clear in your own mind that A and B are mutually exclusive. 



Let me take an example and suppose 



(1) That the energy of muscular contraction in the long run 



depends in some way on the oxidation of sugar; 



(2) That in the absence of an adequate supply of oxygen the 



reaction 



CJl.^O, -f 6 O^ = 6 CO^ + 6 H^O 



cannot take place in its entirety ; 

 (31 That under such circumstances some lactic acid is formed as 

 well as carbonic acid; 



