SPECIFIC OXYGEN CAPACITY 



53 



In the present state of our knowledge it is by no means a foregone 

 conclusion that the desirable relationship which we have described 

 should exist. Presumably it depends upon a correspondence between 

 the properties of the particular globin which is present in the 

 haemoglobin and the conditions which are to be found in the blood ; 

 and it seems possible that some slight change in the nature of the 

 globin might produce a hsemochromogen which was much less likely 

 than that of the normal body to go completely to haemoglobin. There 

 would be an appreciable quantity of iron in excess of oxygen. If, on 

 the other hand, the excess of iron is not measurable, it follows that 

 the background of iron-containing bodies is inappreciable in mass 

 and is only of theoretical interest. 



Much laborious work has been done on the determination of the 

 "specific oxygen capacity" of haemoglobin. Suppose, for instance, 

 that it appears as the result of analysis that 401 cubic centimetres 

 of oxygen correspond invariably to a gram of iron, it would follow 

 that haemoglobin obeyed the law of definite proportions so far as 

 oxygen and iron were concerned, and also that it obeyed the law of 

 combination in simple proportions. For expressing this ratio of the 

 iron to the oxygen by weight every 56 grams of iron would corre- 

 spond to 32 grams of oxygen. In other words the oxygen and the 

 iron would be united in the proportion of one atom of iron to two 

 of oxygen. 



The following table will, however, show that the history of the 

 subject provides us with but scanty hope of reaching this ideal. 



The discrepancies between the various analyses amount in some 

 cases to one-third of the whole quantity of oxygen measured, and 



