184 HEMOGLOBIN 



cent, saturation. Down to that point Fig. 62 shows (a) a dissociation 

 curve calculated from Hill's equation {n= 1-32), (6) points calculated 

 from the data given in the second experiment of Barcroft and Hill. 

 It will be seen that the points fall on a reasonable dissociation 

 curve for the haemoglobin. 



From the other ciunre of reduction given in the paper (5) a dissociation 

 curve can be extracted of much the same type as that in Fig. 62. 

 It would be interesting to repeat and see whether the dissociation 

 curve of the solution determined by the bubbling method agreed 

 with that actually found by the normal method of equiUbration. 



The above results, however, seem to show that the increase in the 

 rate of reduction on the rise of temperatiu'e is in fact ruled by the 

 temperature coefficient of the oxygen dissociation curve, which would 

 appear therefore to be between 3 and 4. 



The effect of rise of temperature, then, is to drive oxygen out of 

 haemoglobin, other things being equal; that statement carries with 

 it by implication another, namely, that when oxygen is driven out 

 of haemoglobin heat is absorbed, or to put it the other way, when 

 oxygen unites with haemoglobin heat is given out. It is naturally 

 a matter of some interest to determine the amount of heat given 

 out when a molecule of oxygen unites with an equivalent of haemo- 

 globin. This may be determined experimentally, it may also be 

 calculated from the oxygen dissociation curve. It seems better first 

 to consider the latter method because the reader will see what 

 opportunities there are for a want of imiformity in the final answer. 

 The fact is, as will appear later, that different workers have found very 

 different values for the heat of formation of oxyhaemoglobin, and in 

 considering them it is as well to be aware of the extent to which a want 

 of uniformity may reasonably be looked for. Therefore, to take the 

 matter up thermodynamically (if I may use so resonant a word to 

 describe any process of treatment to be found in these pages), con- 

 ceive of a solution of haemoglobin in equiUbrium with oxygen and, 

 say, 64 per cent, saturated at a certain temperature, say 26° C, the 

 oxygen pressure is, according to Fig. 57, 12-5 mm. ; now gradually raise 

 the temperature ; in order to prevent the saturation f aUing the oxygen 

 pressure must be raised also, and at 38° C. the pressure will be 31 ram. 

 The heat of combination (Q) of one molecule of oxygen at that par- 

 ticular percentage saturation is found as follows : 



Q = 2303 xRx j^^^- X log^^ 



