THE BLOOD. 247 



Since the results of these investigations show that con- 

 siderable variations occur under normal conditions, extreme 

 variations alone can be regarded as being of importance. 



An increase in the number of red corpuscles has been 

 observed in serious general diseases with fatal termination: 

 pulmonary gangrene, angina, pleuro-pneumonia. 



A decrease in the number of erythrocytes occurs in essen- 

 tial anemia, hydremia, leukemia, and particularly in per- 

 nicious anemia. 



Shape of the red blood corpuscles. We usually group 

 them as follows : 



1. Normal red corpuscles, without nucleus. 



2. Nucleated erythrocytes. 



a. Normoblasts of normal size. 



b. Megaloblasts, two or three times the size of nor- 



mal red corpuscles. 



c. Gigantoblasts, still larger than the megaloblasts. 



d. Microblasts, smaller than the normoblasts. 

 When the normal blood corpuscles deviate from their 



usual biconcave form they are called poikilocytes. Similarly 

 altered nucleated red corpuscles are called poikiloblasts. 



The red corpuscles frequently undergo considerable 

 change in form in the course of preparation for microscopic 

 examination. This must always be borne in mind when dif- 

 ferentiating between the different groups. 



Varieties of the white corpuscles. According to Ehr- 

 lich and his pupils the white corpuscles are classified as fol- 

 lows: 



1. Lymphocytes. These are from 6 to 9 micra in diam- 

 eter, with a single, large, well-defined nucleus containing an 

 abundance of chromatin. They stain with basic aniline 

 dyes, the protoplasm absorbing more of the stain than the 

 nucleus. 



2. Large Mononuclear Leucocytes. These are 12 to 

 15 micra in diameter, contain a large, not well-defined sin- 

 gle nucleus with little chromatin, and homogeneous, baso- 

 phile protoplasm. 



