154 THE PRINCIPLES OF IMMUNOLOGY 



Functions of Phagocytosis. Phagocytosis plays an important part 

 in the entire life of the mammalia, even though the differentiation of 

 many cells excludes them from this function. The destruction of 

 erythrocytes in spleen, liver and bone marrow is in part due to phago- 

 cytosis. Involution of the uterus after pregnancy, involution of senile 

 ovaries, decrease in substance of the brain and other organs in old age 

 are due to phagocytosis. Metchnikoff has laid considerable stress upon 

 the activity of phagocytes in the atrophic processes of old age. Rind- 

 fleisch claims to have demonstrated that phagocytes are active in the 

 breaking down and removal of gouty deposits in and about joints. The 

 fixed tissue phagocytes which play a part in the physiological destruc- 

 tion of red blood-corpuscles have been designated by Kyes as 

 hemophages. In various animal species the blood destruction accom- 

 plished by the hemophages may be carried on predominately in one 

 organ or another, the site of destruction, however, being constant for 

 a given species under normal conditions. Pearce and his co-workers 

 have shown that extensive blood destruction increases the phagocytic 

 activity in the spleen and liver. They have also shown, as has been 

 confirmed by us, that the removal of the spleen results in an assump- 

 tion of hemophagocytic activity by the endothelial cells of the lymph- 

 nodes. Gary has demonstrated that the injection of foreign red 

 blood-corpuscles markedly increases the hemophagocytic activity of the 

 recipient, not only in the spleen, which normally plays the important 

 part in destruction of the red cells, but also in other organs. The 

 resistance of the organism to foreign bodies, either living or inert, 

 is partly the result of the same process. 



Under abnormal circumstances the removal of tissue and cell 

 detritus is due in part to phagocytosis. In the inflammatory reaction 

 following the introduction of foreign bodies, especially infective bac- 

 teria, phagocytosis is the first line and most important defensive 

 mechanism against invasion. Dusts inhaled into the lungs are taken 

 up by mononuclear phagocytes or macrophages and conveyed to neigh- 

 boring lymphatics and lymph-nodes, thus preventing accumulation on 

 the respiratory membrane. In inflammation the circulation is slowed 

 in the small vessels of the neighborhood, thus permitting the accumu- 

 lation of leucocytes on the inner wall of the vessels. They then migrate 

 through the vessel walls by ameboid movement and because of chemo- 

 tactic attraction continue through the tissues to the irritating sub- 

 stances. If the latter are bacterial the leucocytes attempt to ingest 

 and destroy them. Thus it can be seen that phagocytosis is an im- 

 portant process in the normal physiology of the body and perhaps 

 even more so in the pathological physiology of defense against disease. 



The material to be ingested by phagocytes in part determines the 

 type of cell which participates. The microphages are especially active 

 in taking up bacteria, whereas the macrophages are active in ingesting 

 inert tissue detritus. Nevertheless, macrophages often take up bacteria, 

 as in tuberculosis, and, as has been shown by Kyes, by Bull and by 

 Hopkins and Parker, pneumococci, typhoid bacilli and streptococci are 



