THE STORY OF THE BACTERIA. 13 



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 

 self-built, cellular mechanism ; that, 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 universal principle in nature ; that the doc- 

 trine 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. 



