THE MICROSCOPE IN MEDICINE AND SANITATION. 113 



when red cells arc to be counted. For counting white 

 cells the blood is diluted with 10 parts of \% 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 



Fig. 44. — Blood-cells (Wright's Stains). (Photomicrograph by W. C. 

 Greene, Harvard Medical Schoo|.) (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 anaemia the red cells may fall to 

 360,000 per cubic millimeter and in other conditions they 

 may much exceed the normal. Leucocytosis, or the in- 



