192 



THE ARMY FOR HOME DEFENCE 



lipide membrane surrounding the specialised cell (p. 51). As 

 the major length of the cholesterol molecule is fat soluble, the 

 tendency will be for the OH group to be pulled close to the surface 

 of the cell. In this position the hydrophilic cell-substance will 

 enter into competition with the surrounding plasma for the polar 

 group. The balance between Ca and K plays a very important 

 part in this tug-of-war. If the blood Ca is on the low side and the 

 cholesterol high {e.g., in starvation or diabetes) the cell contents 

 win, and the cholesterol and other fatty bodies are tucked away 

 in the cell. On the other hand, when the calcium is high (or K 



Afferent 

 vessel 



Efferen-t 



\'essel 



Glomerular 

 capsule 



CapillAT-^" 

 tuft 



Capsule 



Tubule 



VlG. 46. — IJianrain of Jiaipinhian porisust-k'. (From Ciisliny's Secretion of Urine.) 



low) the tendency is for the cholesterol to form aggregates with 

 some calcium soap as nuclei (p. 107) and gall-stones may be 

 formed. 



One of the most important functions of the reticulo-endothelial 

 system is hsemolyto-poietic. This is especially developed in bone 

 marrow, spleen, liver, and lymph nodes. These organs are rich in 

 sessile reticulo-endothelial cells, having the role (in bone marrow) 

 of forming or of destroying erythrocytes, and in the others of 

 destroying them (q.v.). 



Ultimately the ingested particles or their derivatives are carried 

 by wandering cells to the liver and excreted with the bile into 

 the gut. That is, the heavy metals, the colloidal dyes and dis- 

 integrated blood pigment are eliminated with the f£eces (q.v.). 



