148 UNCONSCIOUS NERVOUS OPERATIONS 



202. Structure of the Blood. Under the microscope the 

 blood is seen to consist of a nearly colorless fluid, the 

 plasma, in which float cells of two sorts, called from their 

 color the red and the white (or colorless) corpuscles (Fig. 

 17, p. 26). Ordinarily there are several hundreds of red 

 corpuscles to one of the white corpuscles, and to them the 

 color of the blood is due. 



203. The Quantity of Blood in the human body is esti- 

 mated at about one thirteenth the body's total weight, or, 

 in a person of average size, about one and a quarter 

 gallons. Any deficiency of blood in the body (as from 

 hemorrhage), is soon supplied by the passage of water 

 from the tissues to the blood by means of the lymph 

 ( 209), and an excess is removed by the transfer of 

 water to the tissues, and by the secretion of the kidneys. 

 Thus the quantity of blood in the system is practically 

 invariable. 



204. The Red Corpuscles are unnucleated cells, all of 

 nearly the same size about -$^$ of an inch in diameter, 

 and one fourth of that in thickness. They are round and 

 flat, but slightly thicker at the edge than in the middle. 

 Being flexible and elastic they are bent out of shape as 

 they are crowded together in the current, but resume 

 their usual form when the pressure is removed. They 

 have a close, colorless, spongy framework, the stroma, 

 while by far the larger part of their substance is a red 

 coloring matter in the meshes of the stroma, called hemo- 

 globin. This is the useful part of the corpuscle, the 

 stroma apparently having only the office of holding the 

 hemoglobin in convenient shape. 



205. The Formation of the Red Corpuscles is found to take 

 place in the red marrow of the bones. The peculiar tissue 

 called red marrow is richly supplied with blood vessels 



