GENERAL BACTERIOLOGY 
79 
7,000-8,000 per cu. mm., and that of blood platelets is 
300,000 per cn. mm. 
While the erythrocytes are all alike—just as the blood 
platelets are all alike—the leucocytes are of seven dif¬ 
ferent kinds, as follows: 
1. Polymorphonuclear leucocytes or neutrophiles: 
these constitute about 70 per cent of all leucocytes. 
2. Small lymphocytes make up 20 per cent. 
3. Large lymphocytes—about 3 per cent. 
4. Large mononuclear leucocytes—about 3 per cent. 
5. Transitional leucocytes—about 2 per cent. 
6. Eosinophile leucocytes—about 1 per cent. 
7. Basophile leucocytes or mast cells—about 1 per 
cent. 
Generally speaking, in most infections there is an in¬ 
crease in the number of leucocytes—leucocytosis, al¬ 
though in a few acute infectious diseases the reverse is 
the rule, the leucocytes being diminished—a condition 
called leucopenia. 
Leucopenia occurs, quite characteristically, in ty¬ 
phoid fever, tuberculosis, malaria, dengue, measles, in¬ 
fluenza, and such tropical diseases as Kala-azar. 
Leucocytosis occurs with especial regularity in pneu- 
mococcic, septic (streptococcic and staphylococcic), 
meningococcic and colon bacillus infections. 
What is just as important as, or even more important 
than, the white cell count (to determine the presence 
of leucocytosis or leucopenia) is a differential count by 
which is understood the counting of the percentages of 
the various leucocytes in a stained blood film prepa¬ 
ration. 
Again, in a general way, one may say that in acute 
infections the neutrophiles are increased while in a 
chronic infection the lymphocytes are (the neutrophiles 
