GENERAL BACTERIOLOGY 
67 
importance is ascribed to body fluids (humoral is from 
Latin humor, meaning fluid). 
1. Metchnikoff’s Cellular Theory, or Phagocytosis.— 
This theory is based on Metchnikoff’s earlier observa¬ 
tions that ameba (a unicellular organism) when about 
to receive its nourishment would flow about the food 
particle, surround and engulf it, and then ingest it, and 
under the microscope the gradual disappearance of the 
food particle could be observed. 
Metchnikoff next observed that, when anthrax bacilli 
were injected into frogs, leucocytes (which possess 
ameboid movement) would engulf and destroy the 
bacilli. This line of observations, continued in the 
animals and human beings, soon left no room for doubt 
that a similar process frequently took place; in fact, 
the actual engulfment and disintegration of gonococci, 
meningococci, staphylococci, and pneumococci is easily 
demonstrable. 
Metchnikoff divides the phagocytic cells into two 
groups: 1. Macrophages (“big eaters”) which are 
large mononuclear leucocytes and certain fixed tissue 
cells, such as those lining serous cavities (pericardium,* 
peritoneum, ## and pleura,f) cells of the spleen, lymph 
glands, etc. This takes place especially in chronic in¬ 
fectious diseases, such as tuberculosis, syphilis, etc. 
2. Microphages (“small eaters”) are chiefly polymor¬ 
phonuclear leucocytes, t they are especially concerned in 
acute infectious diseases, such as meningitis, etc. 
Among the substances mentioned under the anti- 
♦Pericardium is the sac in which the heart is found. 
♦♦Peritoneum is the lining of the abdominal cavity. 
tPleura is the covering of the lungs. 
tLeucocytes (the white blood cells) are of five kinds: 
1. Small mononuclear leucocytes (contain one nucleus). 
2. Large mononuclear leucocytes (contain one nucleus), 
3. Polymorphonuclear leucocytes (contain one nucleus), 
4. Basophile leucocytes (granules stain blue). 
5. Eosinophile leucocytes (granules stain red). 
