BLOOD SYSTEM. 



349 



(b) White Globules {Leucocytes). — These are much fewer 

 in number, being on an average only about one in eight 

 hundred. They differ from the red in color, being color- 

 less ; in size, being a little greater in diameter ; in shape, 



Fig. 236. — Different forms of leucocytes. 



being normally spherical instead of disk-shaped ; in 

 structure, being distinctly nucleated ; and, last and most 

 important of all, in being living cells, endowed with 

 amoeboid movement — in fact, in having all the properties 

 and capacities of living protozoa, crawling about like 

 living things. Some of the shapes which they take on 

 are shown in Fig. 236. 



(c) Blood Plates. — These are very much smaller than 

 either of the others. They are difficult of demonstra- 

 tion, and their function is doubtful. In fact, they are 

 believed by some investigators to be not true blood 

 elements at all, but only the disintegrated remains 

 of wornout white corpuscles. This is still under dis- 

 cussion. 



Chemical Composition.— The globules of blood 

 seem to be composed of an albuminoid stroma, colored 

 in the case of the red, with another peculiar albuminoid 

 substance— haemoglobin. This substance contains a nota- 

 ble quantity of iron, and has a remarkable relation to 

 oxygen. It readily takes up oxygen, and as readily 

 gives it up again, and in doing so changes color. In 

 an oxidized condition (oxyhemoglobin) it is intensely 

 scarlet red. In the deoxidized condition it is dark-pur- 

 plish red. 



