THE MICROSCOPE IN MEDICINE AND SANITATION. 113 
when red cells are to be counted. For counting white 
cells the blood is diluted with 10 parts of 4% acetic acid 
tinted with gentian violet, which destroys the red cells 
and faintly stains the white corpuscles. 
Wide variations of the blood elements, both in absolute 
numbers and in proportions, occur in many normal and 
Fic. 44.—BLOopD-CELLS (WRIGHT’S STAINS). (Photomicrograph by W. C. 
Greene, Harvard Medical School.) (Erythrocytes, large basophiles, 
polymorphonuclear neutrophiles, and blood plates.) 700 diameters. 
abnormal conditions. The blood of the adult human being 
should contain 5,000,000 erythrocytes per cubic millimeter 
in the male and 4,500,000 in the female and 3000 to 
10,000 white blood-cells, of which 70-72% should be 
polymorphonuclear neutrophiles, 25-30% basophiles, and 
1% eosinophiles. In anemia the red cells may fall to 
360,000 per cubic millimeter and in other conditions they 
may much exceéd the normal. Leucocytosis, or the in- 
