8 HUMAN PHYSIOLOGY 



cells is formed and pushed upwards, the outermost 

 layers become dried and scale-like, and are given off 

 from the surface of the skin in large numbers, being 

 worn away by the friction of our clothes, and also 

 being removed in the act of washing. The history 

 of a skin cell therefore indicates in a measure the 

 history of many of the living units of our body. 

 They begin as living vital structures, and pass, as 

 the body itself does, through a stage of decline and 

 finally of death. Included in the living substance of 

 a cell we usually find a solid particle termed the 

 nucleus, and attached to or imbedded in the surface 

 of this latter a smaller particle termed the nucleohis. 

 These are highly important structures, which, 

 however, need not further be alluded to in the 

 present instance, save to remark that they are 

 closely connected with the production of new cells. 

 Many cells, in addition, possess a cell wall or 

 boundary-membrane, although this last item does 

 not appear to be an essential characteristic of many 

 of the living units of our frames. 



THE WORK OF CELLS. Recognising the cell as 

 a living structure in its most typical aspect, we must 

 further note that every important organ and tissue 

 of our frame is composed of cells. Naturally, as in 

 a State there are different grades of citizens, some 

 performing work of a higher grade than others, so 

 in our bodily constitution, we find that whilst the 

 whole duties of the body are performed through the 

 work of these wonderful cells, there naturally appear 

 variations in the relative importance of our living 

 units. The cells which compose the outer layer 

 of the skin are thus relatively unimportant as 

 compared with, say, the cells of which the liver is 

 composed, or when compared with those which 



