RETICULOENDOTHELIAL SYSTEM 191 



(suspensoids or emulsoids) have been grouped together under the 

 name of the reticulo-endothehal system. They are found in the 

 hnigs, spleen, hver, bone-marrow, lympoid tissue generally, and 

 in the blood. 



Function. They have a special avidity for aeid suspensions 

 (colloids, small particulate suspensions, fat-dust, cholesterol, 

 bacteria and fragmented and moribimd erythrocytes). Those that 

 are free in the blood stream, e.g., monocytes (histiocytes) and endo- 

 theliocytes, are electrically charged bodies at the hydrogen ion 

 concentration of the blood (pH 7-4) and move to the cathode in an 

 electric field. The bacteria in a suspension of B. typhosus move to 

 the anode. When the smaller electro- negative colloidal mass 

 (bacterium) comes within the sphere of influence of the larger 

 oppositely-charged mass (histiocyte) the result is adsorption and 

 ultimately absorption. The processes whereby bacteria are 

 engulfed are hastened by a gathering together of the bacteria into 

 clumps which may be absorbed as such. The large cell thus 

 disposes of a larger number of the smaller cells at each encounter. 

 Agglutination (the clumping of bacteria) bears a general resem- 

 blance to the process of sensitisation of hydrophilic colloids. In this 

 connection it is interesting to note that the salts of the plasma 

 are essential for the process. If, by means of dialysis, they are 

 reduced appreciably, or if their balance is markedly disturbed 

 agglutination does not take place, and thus bacterial absorption 

 remains a slow process. 



It has been mentioned above that the cells of the reticulo- 

 endothelial system show a special preference for acidic dyes, e.g., 

 trypan blue or pyrrol blue, and thus have become known as 

 " pyrrol " cells. Compare with this the staining action (adsorp- 

 tion) of these dyes on colloids (p. 95). Solid particles may also 

 be taken up by these cells. The special endothelial cells of the 

 lung may be found full of carbon particles, silica powder, asbestos 

 dust, or finely divided metal in animals to which these substances 

 have been administered either by insufflation or by injection (cf, 

 protection of suspensoids by hydrophilic colloids, p. 93). 



Substances of a fatty nature or substances soluble in fats tend to 

 collect, under certain conditions, in reticulo-endothelial cells. 

 The esters of the monohydric alcohol, cholesterol, may, in this way, 

 fill the reticular cells of the spleen to such an extent that that 

 organ undergoes enlargement. We can again, as a first a])j)roxima- 

 tion, suggest that lipide and reticulo-endothelial cells dilTer some- 

 what in electrical charge and thus tend to come more closely 

 together. The lipide may then be oriented in the first instance, 

 so that its polar group is in the plasma and its fatty portion in the 



