46 MAN, THE ANIMAL 



cell wall of higher plants which is composed of 

 cellulose. Their diminutive size prevents one 

 from learning very much about internal parts. 

 There is no distinct nucleus. 



Their method of reproduction is similar to that 

 of the ameba, figure 12. When a bacterium has 

 reached mature size, it begins to form a constric- 

 tion in the middle of the cell which proceeds until 

 the cell protoplasm is completely divided. The 

 two parts separate and two new bacteria are made. 

 A generation, then, among bacteria is from one 

 division of the cell to the next one. This time is 

 often very short, from twenty to thirty minutes, 

 which makes it possible for the bacteria to multiply 

 very rapidly and is the main explanation of why 

 these microscopic plants are capable of producing 

 such remarkable transformations in nature. 



Much study has been given to the feeding habits 

 of bacteria and we have come to appreciate that 

 some live like animals, some have synthetic powers 

 similar to green plants, while others are able to 

 subsist in more primitive forms of energy com- 

 binations than either animals or plants. 



In their methods of living they reveal no new 

 basic principles but do show some special adapta- 

 tions that enable them to render man an invaluable 

 service. 



The chemical analysis of the biological unit, 

 wherever it exists, yields the same chemical ele- 



