STRUCTURE AND FUNCTIONS OF BLOOD AND LYMPH 299 



sons suffering from this condition usually have little or no color, 

 and because the oxygen-carrying mechanism of the Body is be- 

 low normal there is a loss of bodily strength and endurance. The 

 condition is more common between the ages of twelve and twenty 

 years than at other periods, and in girls than in boys. It is not 

 always easily overcome and should have the care of a physician. 

 An outdoor life and plenty of nourishing food, in which iron con- 

 taining substances are included, are beneficial in such cases. 



Origin and Fate of the Red Corpuscles. Mammalian red 

 corpuscles are cells which have lost their nuclei. In the red mar- 

 row of certain bones is the so-called hematopoietic (corpuscle- 

 forming) tissue where red corpuscles are constantly being formed. 

 The cells of this corpuscle-forming tissue are continually multi- 

 plying by mitotic division (see Chap. II), and the daughter cells 

 thus formed store up within themselves hemoglobin, lose their 

 nuclei, either by disintegration or extrusion, and are cast off into 

 the blood stream. It is not known how rapidly they are formed, 

 nor how long any individual corpuscle remains actively at work 

 in the blood stream; but it is known that sooner or later the red 

 corpuscles become worn out, and disintegrate; the hemoglobin is 

 decomposed in the liver in such fashion as to save the iron, and 

 the residue is converted into the bile pigments and excreted (see 

 Chap. XXXI). 



After hemorrhage or as the result of certain pathological con- 

 ditions the rate of production of red corpuscles may be much 

 increased. When. this occurs some corpuscles are liberated into 

 the blood stream in an immature condition, and so the blood will 

 be found at such times to Contain nucleated as well as non-nucleated 

 red corpuscles. 



In the human embryo the labor of making red corpuscles is 

 shared by many of the organs of the Body, notably the liver and 

 spleen. 



The Spleen. This large and conspicuous abdominal organ 

 (L, Fig. 134) has presented to physiologists a problem of classi- 

 fication, in that its function has been and still is so obscure as to 

 cause uncertainty under what general heading it should be dis- 

 cussed. The most satisfactory present view assigns it a function 

 in connection with the blood, and it will, therefore, be described 

 here. The spleen consists of an outer coating or sheath of con- 



