THE HEART AND CIRCULATION. 119 



color, which have a tendency to form in rouleaux. 

 They are homogeneous, with no limiting membrane, 

 and are made up of a fine network of tissue, the stroma, 

 in which is embedded the hemoglobin or coloring mat- 

 ter. This hemoglobin is a crystalline body and the 

 most complex substance known to chemists. The cor- 

 puscles are very flexible and can squeeze through small 

 apertures, as in the tiny capillaries, and regain their 

 shape. They are probably formed chiefly in the red 

 bone marrow at the ends of the bones, which under the 

 microscope shows red corpuscles in various stages of 

 growth, and also in the spleen, for which no other use 

 is known. Their function is to carry oxygen, which 

 forms a chemical combination, though an extremely 

 loose one, with the hemoglobin. As the tissues are 

 more greedy of oxygen than is the hemoglobin, they 

 rob the corpuscles of it. 



FIG. 46. Various forms of leucocytes: a, Small lymphocyte; 6, large lympho- 

 cyte; c, polymorphonuclear neutrophile; d, eosinophile. (Leroy.) 



The white corpuscles or leucocytes are much fewer in 

 number, about one to from 300 to 700 of the red, the 

 average number being 5,000 to 10,000 to the cubic milli- 

 meter. They are larger than the red corpuscles, color- 

 less, and spherical when at rest. Their structure is more 

 definite, there .being a definite cell substance or proto- 

 plasm and one or more nuclei, which vary more or less 

 in shape and size. The corpuscles are classed in accord- 

 ance with these variations in the nuclei. They are 

 most numerous during digestion and are probably formed 

 in the lymphatic system, constantly passing from the 

 lymphatics to the arteries and veins. For they have 



