606 XIII. HEMOGLOBIN AND PORPHYRIN SYNTHESIS 



carnivorous mammals is about the same as that of man, while that 

 of herbivorous animals is lower, 11-12 g. per 100 ml. (2'234-). There 

 is a slight diurnal variation of the hemoglobin concentration, prob- 

 ably caused by excitement and splenic contraction (1802,1969). 



The ''color index," which has been obtained by rather uncertain 

 assumptions about what constitutes a "normal" hemoglobin content 

 and erythrocyte count, should be discarded and replaced by the 

 mean corpuscular hemoglobin, which is obtained by dividing the 

 grams of hemoglobin per 1000 ml. of blood by the number of millions 

 of erythrocytes per mm.' of blood. It states the number of micro- 

 micrograms (10^- g.) of hemoglobin in a single erythrocyte and is 

 normally about 30. 



The mean corpuscular hemoglobin does not indicate whether an 

 abnormally small or high value is due to a change of hemoglobin 

 concentration in the cell, or to a variation in cell size. The concen- 

 tration of hemoglobin in the cell is given as mean corpuscular hemo- 

 globin concentration, which is obtained as a percentage by dividing 

 the number of grams of hemoglobin per 100 ml. of blood by the 

 volume of packed red cells per ml. of blood. The normal value is 

 35%. The mean corpuscular hemoglobin concentration is remarkably 

 constant even in animals of different species, in spite of variations 

 in size and number of erythrocytes {3102). Hyperchromicity of cells 

 in the true sense of increased mean corpuscular hemoglobin concen- 

 tration does not exist; the increased mean corpuscular hemoglobin 

 of erythrocytes found, for instance, in pernicious anemia is simply 

 due to the larger size of the cells. "Hypochromicity" may be due to 

 a small cell size, or may be due to a smaller concentration of hemo- 

 globin in the cell (true hypochromicity), or to both. The finding of 

 an abnormally small mean corpuscular hemoglobin concentration is 

 of importance since it indicates that hemoglobin formation is impaired 

 to a greater extent than red cell formation. 



At birth the hemoglobin content of the blood is very high (20-22%). 

 While most workers assume that this is due to polycythemia, Wintrobe 

 (3103,3104,3106) finds the erythrocyte count not above five million, and 

 believes that the high hemoglobin content is largely due to the presence of 

 large cells (cf. also Chapter XI, Section 6.5.). In Australia, Hicks (1271) 

 found the average hemoglobin content at birth 22.3% and the average ery- 

 throcyte count 6.95 million.* During the first months or the first year of life 

 the hemoglobin falls to a minimum of about 11 gram per cent, partly owing 



* Smith {2575a), in the United States, gives somewhat lower values: hemoglobin, 

 20 g. per 100 ml.; erythrocytes, 5.5 million. 



