96 HEMOGLOBIN. 



the Corpuscles. In the drop of blood examined under the 

 microscope, the Plasma occupies the clear spaces between the 

 corpuscles. The corpuscles make up one-third of the bulk of 

 the blood, and the plasma the other two-thirds. The plasma 

 consists chiefly of water, having in solution various salts, in- 

 cluding common salt; it also contains the nourishing mate- 

 rials for the tissues. These nourishing materials have been 

 obtained from the food by digestion, and consist chiefly of 

 Proteids, Fats, Sugar. The plasma also contains waste mat- 

 ters on their way out of the body. How the food is prepared 

 for the building of tissue, and how the waste matter is removed 

 from the body, we shall study a little later. 



The difference in color of an individual corpuscle and the 

 blood in the mass may be better understood by comparing it 

 with something that we see more frequently. A tumbler of 

 currant jelly has a rich, red color, but a thin layer of the 

 same jelly, as when one takes a spoonful on a plate, has a 

 pale color, more yellowish. The colorless plasma with the 

 colored bodies in it may be compared to a glass dish filled 

 with cranberries and water. 



The coloring matter in the blood, then, is wholly in the 

 colored corpuscles. Examination of these corpuscles shows 

 that their color is due to a substance called Hemoglobin. 

 There is a small amount of iron in the hemoglobin, and the 

 presence of this small quantity of iron appears to be essential 

 to give the blood its color. When we come to the study of 

 respiration we shall see that the hemoglobin in the corpuscles 

 is the chief agent in picking up the oxygen from the air in 

 the lungs and carrying it to the tissues in the body. 



It will be well here to examine again the flow of blood in 

 the capillaries of the frog's web. It will be seen occasionally 

 that when one of the' colored corpuscles is pressed against an 

 angle at the forking of the blood stream, it is sometimes bent, 



