BLOOD. 



477 



In the animal body haemoglobin is never saturated with oxygen, 

 even in arterial blood, while oxyhemoglobin is never absent from venous 

 blood ; consequently, physiologically, we have to deal with an association 



of haemoglobin with oxyhemoglobin, the relative proportions of each 

 varying in different localities and under different circumstances. 

 Further characteristics of these bodies will be studied in the chapter on 

 Respiration. 



