THE RETICULO-ENDOTHELIAL SYSTEM 93 



The functions of the cells of the rcticulo-cndothelial system may 

 be summarized as follows : — 



1. The macrophages engulf senile and injured red cells and 

 erythrocyte fragments and thus participate in their removal from 

 the circulation, from areas of infection, and from the tissues where 

 extravasation has occurred. 



2. They phagocytize and destroy dead and dying leucocytes and 

 injured tissue cells. 



3. They phagocytize inert foreign material such as deeply in- 

 haled dust and also carbon particles, India ink, and acid colloidal 

 dyes gaining entrance to the blood stream, thus removing them from 

 the circulation. 



4. In inflammatory and degenerative conditions of the nervous 

 system phagocytic cells, according to Hadficld and Garrod, remove 

 the free myelin and its disintegration products. 



5. According to Bunting (1938), in certain chronic infections 

 the macrophages form the epithelioid cell which in addition to its 

 property of phagocytosis is able to secrete a precollagenous reticu- 

 lum (Miller) that aids in localizing infection. 



6. The macropliages may fuse and form the foreign body giant 

 cell and thus be able to interpose a mass of protoplasm Ijetween the 

 tissue cells and a body too large to be engulfed. 



7. According to Mann and Higgins (1938) and Hadfield and 

 Garrod (1938) one of the functions of the fixed histiocytes in the 

 liver is the metabolism of the blood pigments leading to the re- 

 tention and return to the bone marrow of the iron liberated from 

 the disintegrating red cells and the excretion of the iron-free por- 

 tion as bile pigment. 



8. These same authors also state that the liver histiocytes to- 

 gether with the liver cell seem to act as a functional unit in lipid 

 metabolism, 



9. According to Sabin (1939) and Bunting (1938), there is some 

 evidence suggesting that the cells of the reticulo-endothelial system 

 help in maintaining the normal composition of the plasma pro- 

 teins. 



10. There is a great deal of evidence indicating that antibodies 

 are produced perhaps entirely by cells of the reticulo-endothelial 

 system. This view was held by Metchnikoff. 



