THE BLOOD CELL 93 



methods of determining the approximate amount present. The amount 

 of hemoglobin present in a quantity of blood is usually determined 

 colorimetrically by comparing the color of the blood with standard col- 

 ors which correspond to known strengths of hemoglobin. In normal 

 persons the amount of hemoglobin varies greatly at different ages, and 

 in order to determine whether or not a given blood contains more or 

 less hemoglobin than normal, it is imperative to consider the age. The 

 greatest variations occur between birth and the sixteenth year. After 

 the sixteenth year the blood in males usually contains a larger amount 

 than that in females (Williamson 4 ). Instruments used in determining 

 the amount of hemoglobin should be standardized to give the value in 

 grams hemoglobin per 100 c.c. of fluid. 



The amount of hemoglobin which is present in each corpuscle in 

 terms of normal is therefore of some clinical interest. This relation of 

 the number of red cells to the amount of hemoglobin is known as the 

 color index and is computed as follows: The average red count in man 

 is 5,000,000 to the c.mm., and the average minimal amount of hemo- 

 globin is taken as 13.88 grams in 100 c.c. of blood (=80, Sahli; =90, 

 Miescher; =86, Plesch; and 110, Tallquist methods). These relative 

 values give a color index of one. The percentage of normal red cells 

 divided by the percentage of normal hemoglobin present gives the 

 color index. 



The Origin of the Red Blood Cells 



In fetal life the spleen and the liver are generally believed to be re- 

 sponsible for the formation of the red blood cells. In extrauterine life 

 this function is taken over by the red bone marrow. In the primitive 

 condition all red blood cells are supposed to be nucleated. In extra- 

 uterine life the nuclei of the red cells are lost, and nonnucleated forms 

 are alone present in the blood stream. In fetal life and in certain path- 

 ologic conditions, the rate of blood formation is so rapid that some 

 nucleated cells appear in the blood. The normal response of the body 

 to a loss of red blood corpuscles consists in an increased activity of the 

 blood-forming cells of the red bone marrow. It is not easy to follow 

 the course of the regeneration of the red corpuscles or to discover the 

 mechanism of their formation in the bone marrow, since this tissue pre- 

 sents a mixture of cells which are precursors of the varied corpuscles 

 found in the blood and the identity of which can not be determined. 



Recently new methods of staining blood for microscopic examina- 

 tion have allowed more detailed study to be made on the site and 

 method of blood cell formation. When fresh unfixed blood is treated 

 with solutions of various dyes, such as brilliant cresyl blue, polychrome 



