248 DISEASES OF THE BLOOD 



ANEMIA AND THE SPECIFIC ANEMIAS 



The customary division of the anemias is into (a) primary, 

 i. e., those in which the cause seems to depend upon some abnor- 

 mality in the blood-forming organs or in the blood itself; and 

 (6) secondary, embracing anemias the result of some obvious 

 cause, such as hemorrhage, poisoning with blood-destroying 

 poisons, cachexia, etc. In these various forms of anemia 

 certain chemical differences prevail, but they are by no means 

 so striking as are the histological differences in the formed 

 elements of the blood. 1 



SECONDARY ANEMIAS 



As the simplest variety, anemia following a single large 

 hemorrhage may be considered first. 



If loss of blood by hemorrhage is rapid, the effects are natu- 

 rally much more serious than when the loss is slow. The total 

 quantity of blood in the average adult is estimated at about -^ 

 to -^j the total body weight (therefore about 10 to 12 pounds), 

 although this proportion does not hold for extremely obese or 

 extremely thin individuals ; 2 in infants the proportion is lower 

 about 2^5-. When one-third of the total amount of blood is lost 

 rapidly, a marked fall of blood pressure occurs ; loss of one- 

 half of the total amount may be fatal, and loss of more than that 

 at one time usually is fatal. The chief cause of death following 

 large hemorrhages is the low blood pressure rather than the loss 

 of any of the constituents of the blood ; hence the successful 

 results of the use of physiological salt solution after severe hemor- 

 rhage. The number of corpuscles may be greatly reduced after 

 several small hemorrhages, even to as low as 1 1 per cent, of the 

 normal number (Hayem), without fatal results, because in the 

 intervals between the hemorrhages enough fluid has been taken 

 up by the blood to maintain the blood pressure within safe limits. 



After a severe hemorrhage the composition of the blood 

 changes rapidly, for the fluids contained within the tissues and 

 lymph-spaces pass into the blood in large amounts. This helps 

 to maintain blood pressure, but results in the blood containing 

 a larger proportion of water and salts and a smaller amount of 

 proteid and red corpuscles ; the " total alkalinity " also falls, 

 largely because of the scarcity of " fixed alkali," on account of 

 the poverty in corpuscles and blood proteids. The proportion 

 of water increases at first more rapidly than the proportion of 



1 Concerning Iqcal anemia, see " Infarcts." 



2 Haldane and Smith (Jour, of Physiol., 1900 (25), 331) estimate the blood 

 of adults at but -^ of the body weight. 



