74 BLOOD 



2. In fetal life and in certain diseased conditions blood for- 

 mation occurs with sufficient rapidity to permit the immature 

 erythroblasts to gain entrance into the general circulation. The 

 red blood cells of the earliest fetal circulation are therefore all 

 nucleated, those of later fetal life are nucleated in constantly 

 decreasing proportion, while in healthy extra-uterine life only 

 mature non-nucleated forms occur in the general blood current. 



3. The primitive nucleated red cells, the type having been once 

 firmly established in the early fetus, are reproduced by mitotic 

 division of similar parent cells. 



4. Though the size of the primitive cells varies considerably, 

 and is for the most part larger than that of the mature forms, 

 yet prior to their entrance into the general circulation of the 

 adult, all erytlirocytes closely approximate a constant diameter 

 of 7.5/x. 



WHITE BLOOD CORPUSCLES (white blood cells, leucocytes, 

 colorless corpuscles). The white blood cells are nucleated granular 

 masses of protoplasm usually of spherical form but possessing a 

 remarkable tendency to undergo active amoeboid motion, They 

 are of a distinctly viscid consistence, adhering more or less closely 

 to the vascular walls, and therefore lying at the periphery of the 

 blood stream, while in circulation. In microscopical preparations 

 of freshly drawn blood they adhere quite firmly to the glass slide 

 or cover. With moderately high magnification the cytoplasm 

 of the white blood cell is seen to possess fine granules which vary 

 in number and in size in different cells. The greater portion of 

 these cells possess numerous fine granules (neutrophiles) ; a smaller 

 portion show no cytoplasmic granules in freshly prepared speci- 

 mens (the non-granular, "hyaline" or mononuclear leucocytes); 

 occasional cells show very coarse granules throughout their cyto- 

 plasm (eosinophiles). 



All forms of white blood cells possess a nucleus which, how- 

 ever, is only faintly visible in the living cell, but is readily brought 

 into view by the action of dilute acids, which also cause the cyto- 

 plasmic granules to accumulate about the nucleus. The nucleus 

 is likewise brought into view by other laking reagents water, 

 bile, electricity, etc., as well as by hyperisotonic solutions heavy 

 solutions of sodium chlorid, etc. 



Normal blood contains 6,000 to 8,000 white blood corpuscles 

 per cubic millimeter. They are therefore present in the propor- 

 tion of 1 to 600 or 800 red corpuscles. This ratio is, however, 



