ra THE WHITE CORPUSCLES 103 



When the colourless corpuscles are examined chemically 

 they are found to consist chiefly of water, and only 10-12 

 per cent, of solid matter. As in the case of the stroma of 

 the red corpuscles, so here also this solid part is made up 

 largely of proteins or substances closely allied to 

 proteins. But frequently also some small amount of fat 

 is found to be present, as also of a representative of that 

 class of substances known as carbohydrates or starchy 

 bodies, called glycogen, which will be dealt with later 

 on when treating of the liver. (See Lesson V.) 



The parts played by the colourless corpuscles in the 

 animal economy are probably varied and numerous, but 

 our knowledge of them is very imperfect. We have seen 

 (p. 82) that under special circumstances these corpuscles 

 may, by means of their amoeboid movements, migrate in 

 large numbers through the walls of the blood-vessels into 

 the tissues, and it is possible that here they may in some 

 way assist in the removal of the causes which are giving 

 rise to the disturbance. Quite probably a similar migration 

 is taking place on a smaller scale at all times, for some as 

 yet obscure but possibly similar purpose. Again, by their 

 amoeboid movements the majority of colourless corpuscles 

 can flow round small solid particles and absorb them into 

 their cell-body ; in other words they can feed on sub- 

 stances in the blood and thus be continually busied in 

 keeping this fluid in a normal condition, more particularly 

 when, as in disease, the composition of the blood is altered 

 by the introduction of foreign matter such as bacteria, &c. 

 Moreover it is extremely probable that the colourless cor- 

 puscles may act on the blood and on any foreign matter it 

 may at times contain by means other than their amoeboid 

 movements ; namely chemically by the discharge into the 

 blood of substances formed within themselves. Finally 

 there are reasons for supposing that when blood is shed, 

 these corpuscles have something to do with starting that 

 striking change, to which we have already alluded, known 

 as the clotting or coagulation of blood. 



4. Blood Platelets. — In addition to the red and white 



