PART V. GENERAL PHYSIOLOGY 



CHAPTER XII 

 RELATION TO ENVIRONMENT 



Introduction. By physiology is meant the science of 

 function. In Part IV we learned about what bacteria are, 

 and in Part V we are to learn what bacteria do. In con- 

 sidering the morphology of bacteria, one of the striking facts 

 brought out was the simplicity of form. Bacteria are reduced 

 to almost the limit of simplicity so far as form and structure 

 are concerned. Generally speaking, structure and function are 

 related. The organisms which have the most complex func- 

 tions are those which have the most complicated forms. But 

 in the bacteria there is a striking exception to this general rule. 

 The bacteria are very simple so far as their form is concerned, 

 but their functions are very complex, and it is one of the 

 wonders of biology how such a complicated physiology has 

 developed on so simple a morphology. 



Functions. In the subject of physiology we have to con- 

 sider not only the functions of bacteria, that is, what they do, 

 but we have also to consider the effect which the environment 

 has upon the organism and the modifications which these 

 external conditions have on the functions. 



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