CHAPTER XXIII 

 THE CIRCULATION OF THE BLOOD 



IN organisms of microscopic dimensions there is obviously sufficient opportunity 

 for interchange of soluble materials by diffusion, without the necessity for special 

 provision to enable the products of the activity of one organ to reach another 

 organ with due rapidity. With increase in size this is no longer the case, and 

 is especially important with regard to the supply of oxygen. 



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<f*^ /-.^>y ^rv 



vt-tii***?. 



Fl(5. 218. A I'ACE FROM THE REPRODUCTION OF HARVEY'S MANUSCRIPT NOTES. 



(Harvey, 1616, p. 80.) 



Accordingly, we find more or less rudimentary methods of causing iow of 

 body fluids from one part to another in early stages of evolution. 



The objects of such currents, which later become developed into those of a 

 special fluid, the blood, in a system of closed tubes with a pump, the heart, may 

 be said to be, in general, threefold : 



1. The supply of food, inclusive of oxygen, to all parts of the organism. 



2. The removal of waste products of activity, which would paralyse function 

 if allowed to accumulate. 



3. The carriage of chemicai substances from an organ in which they are 



