Aggregation theory 



71 



of oxygen as being the factor which determines the reduction of 

 blood in cold-blooded animals. 



In the opening sentences of this book I alluded to the specula- 

 tions which I sometimes allow myself. I drew a contrast between 

 morphology and biochemistry in their relation to natural selection. 

 The fundamental basis of natural selection is variation, but it would 



100 



10 20 30 40 50 



10 20 30 40 50 



Fio. 38. Dissociation curves of I, haemoglobin in -9 % KC1 in presence of 25 mm. C0 2 at 

 15 C. ; II, ditto in absence of CO,; III, blood at 37 C. exposed to 3 mm. C0 2 ; 

 IV, ditto exposed to 20 mm. CO,. 



seem that the chemical properties are fixed. They are immutable 

 properties of the substance. The reader will not have read the 

 preceding chapters without discovering for himself that a way out 

 of this apparent impasse has been discovered. At all events in the 

 case of the reaction Hb + 0,, 5^ Hb0 2 this is so. 



The velocity of this reaction is dependent to some extent upon 



