The Cells of the Body 13 



These cells have, too, a most important r61e, 

 as we shall see by and by, in combating the 

 incursion of certain forms of bacteria which 

 now and then obtrude themselves into this 

 happy family of cells which makes up the 

 human body. 



We have thus seen that all the varied struct- 

 ures and functions of the human body are but 

 the combined expression of the structure and 

 lives of the cells which compose it, all co-ordi- 

 nated and working in harmony by means of a 

 self -built, cellular mechanism. Starting with 

 the type of the most simple of living things, 

 a single cell, the finished organism is an 

 aggregate of the progeny of the original cell, 

 some groups of which have developed special 

 forms and powers, in accordance with a uni- 

 versal principle in nature. So the doctrine of 

 evolution, even should the record of the rocks 

 be incomplete and perfect continuity in the 

 grouping of living species fail, still finds 

 epitomized in every animal and plant which 

 has escaped from the primitive simplicity of 

 the lowest forms, a most pertinent illustration 

 and convincing proof. 



