508 



ORGAN SYSTEMS OF MAN 



the latter group is difficult to understand. 

 However, it must be admitted that since the 

 red blood cell lives only about 120 days and 

 never reproduces, it would seem to be a 

 waste of effort to utilize the space in the cell 

 for a nucleus when it could be occupied 

 more profitably by hemoglobin, the oxygen- 

 carrying pigment. The erythrocytes possess 

 nuclei when they first form in the red mar- 



unable to supply the cells with the proper 

 amount of oxygen. 



The red cells are formed and destroyed 

 at a tremendous rate, about two and one- 

 half million per second. Destruction occurs 

 in the spleen and other specialized tissues. 

 In a normal person the cells must be pro- 

 duced at the same rate as they are de- 

 stroyed. Since one of the chief elements of 



Fig. 19-14. With a break in the skin, the leucocytes (certain kinds) move out of the blood 

 vessels into the injured area where they engulf and destroy any invading bacteria. Bacteria 

 that are not eliminated by the leucocytes may find their way to the lymph nodes where 

 they are usually destroyed. If, however, they get past these barriers they are free to invade 

 the entire circulatory system and the entire organism. 



row of the bones, but lose them just before 

 entering the blood stream. The cells are a 

 light yellow in color under the microscope, 

 although in combined numbers they render 

 the blood a typically red color. Normally 

 there are from 4,500,000 (women) to 

 5,000,000 (male) cells per cubic millimeter 

 of blood. This number varies with disease 

 and nutritional deficiencies. A drop either in 

 the number of red cells or their hemoglobin 

 content results in anemia, which can be 

 serious if prolonged because the blood is 



hemoglobin is iron, there must be a contin- 

 ual supply in the diet. The amount is small 

 (0.01 gm. per day) and most diets contain 

 an ample amount. However, it is now 

 known that copper is also essential for 

 proper hemoglobin formation. The need 

 for copper lies in the production of an en- 

 zyme necessary for hemoglobin formation. 

 Some serious deficiencies in the bone mar- 

 row cause a drop in hemoglobin produc- 

 tion, resulting in fatal anemias. Recently 

 these have been arrested by administering 



