CHAP. ii.J RESPIRATION. 620 



Thus there arc two main factors in respiration, the respiratory 

 mechanism proper, and the circulation, the one bringing the air to 

 the blood, and the other the blood to the air. We may remind 

 the reader that there is also a third factor, and that one of great 

 moment, the amount of haemoglobin, that is, the number of red 

 corpuscles, in the blood. The amount of oxygen taken up from 

 the lungs depends not only on the strokes of the respiratory and 

 the vascular pumps but also on the richness of the blood in 

 red corpuscles. A body which from loss of blood or from disease 

 is aiuemic is thrown out of breath by very slight exertion, not so 

 much because the respiratory or the vascular pump is weak, but 

 because, through lack of oxygen carriers, with their best efforts 

 the combined pumps can only deliver to the tissues, including the 

 medulla, an inadequate supply of oxygen. And fat persons, whose 

 store of hemoglobin in proportion to their body weight is always 

 below par, are proverbially " scant of breath." 



