STRUCTURE AND FUNCTIONS OF BLOOD AND LYMPH 265 



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 Colorless Blood-Corpuscles or Leucocytes (Fig. 98, F, H, G). 

 The colorless or white corpuscles of the blood are far less numerous 

 than the red; in health there is on the average about one white 

 to three hundred red, but the proportion may vary considerably. 

 Each is finely granular and consists of a soft mass of protoplasm 

 enveloped in no definite cell-wall, but containing a nucleus. The 

 granules in the protoplasm commonly hide the nucleus in a fresh 

 corpuscle, but dilute acetic acid dissolves most of them and brings 

 the nucleus into view. These colorless corpuscles belong to the 

 group of undifferentiated tissues, and differ in no important 

 recognizable character from the cells which make up the whole 

 very young Human Body, nor indeed from such a unicellular 

 animal as an Amoeba. They have the power of slowly changing 

 their form spontaneously. At one moment a leucocyte will be 

 seen as a spheroidal mass; a few seconds later (Fig. 99) processes 



