1 84 The Bird 



the tree merges into limbs, and these into branches, twigs, 

 stems, and at last into the delicate foliage. This last 

 we may liken to the capillaries or hair-tubes in which 

 the blood does its real work of supplying nourishment 

 directly to the tissues, and where it receives the waste 

 matters, carrying them away in its current. 



When we have followed the divisions of a tree out 

 to the foliage, we may find that they touch and interlace 

 with the foliage of another tree, and this is very much 

 like what occurs in the course of the blood. The capil- 

 laries run together and form larger vessels, these in turn 

 coalesce, and soon the blood dark now and filled with 

 the waste matters of the body-cells is flowing through 

 only two large veins (veins always lead toward the heart). 

 These enter the right auricle, which opens into the right 

 ventricle. From here the blood rushes to the lungs to be 

 purified and back again to the left auricle and ventricle, 

 and its cycle is complete. 



If we look at a drop of bird's blood (or that of any kind 

 of warm-blooded creature) under the microscope, we shall 

 see thousands upon thousands of oval discs, or corpuscles, 

 like tiny platters floating in a fluid. These flow about 

 under the cover-glass through little channels, mechanic- 

 ally and very slowly of course, and giving but a faint 

 idea of the way they must tumble and rush after each 

 other through the veins and arteries of the bird. Scat- 

 tered among these oval bodies will occasionally be seen 

 others of indefinite shape and white in colour. As we 

 watch one of these tiny cells, the thought suddenly comes 

 over us, what are birds indeed but collections of untold 



