264 THE HUMAN BODY 



It must be remembered that the liquid part of the blood is 

 subject to changes of volume, either in the way of increase as 

 liquid is received into it from the digestive tract, or decrease as 

 liquid passes from it into the lymph; therefore a variation in the 

 number of red corpuscles per cubic millimeter does not necessarily 

 mean a corresponding variation in the total number in the Body. 



There is a pathological condition known as anemia in which 

 there is a considerable reduction in the number of red corpuscles. 

 This is usually accompanied by a diminution in the amount of 

 hemoglobin contained in each corpuscle, so that as a result there 

 is a serious shortage in the hemoglobin content of the Body. Per- 

 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. 



Hemoglobin. This substance, which is a compound of a pig- 

 ment with a protein (see Chap. I), is the functionally important 

 part of the red corpuscle, the stroma serving merely as a frame- 

 work upon which it is carried. Its importance lies in the fact 

 that it combines readily with oxygen, forming a loose combina- 

 tion which can easily be broken up, thus it serves to transport 

 oxygen from the lungs to the tissues of the Body (see Respira- 

 tion). This property seems to be associated with the presence 

 of iron in the pigment part of the hemoglobin molecule. 



In the adult male about fourteen parts in the hundred by 

 weight of the blood are hemoglobin. It has been estimated that 

 a man weighing 68 kilograms (150 Ibs.) has in his blood 750 grams 

 (1.64 Ibs.) of hemoglobin, which is distributed among some 

 25,000,000,000,000 red corpuscles, giving a total superficial area 

 of about 3,200 sq. meters (3,800 sq. yds.) of hemoglobin. On ac- 

 count of the very rapid circulation of the blood (see Circulation) 

 practically the whole of this great area of hemoglobin is poured 

 through the capillaries of the lungs every thirty seconds, so it is 

 apparent that we have here a remarkably efficient arrangement 

 for supplying the Body with oxygen. 



