FUNDAMENTALS OF BACTERIOLOGY. 



CHAPTER I. 



POSITION-RELATIONSHIPS. 



The student in his biological courses has already learned 

 the necessity of classifying living organisms. The division 

 of the organic world into plants and animals is a very old one. 

 It seems to have been based primarily on ability to move 

 from place to place. Animals could move, plants could not. 

 The first microscopic forms discovered in the seventeenth 

 century were called ''animalcules/' little animals, because 

 many of them could be seen to move. The fact that all 

 organisms are made up of cells and that there are organisms 

 consisting of one cell only was a scientific contribution of the 

 nineteenth century. The term lyrotista is used to include all 

 unicellular organisms; protozoa, the unicellular animals and 

 protophyta the unicellular plants. 



In attempting to decide whether a given organism is a 

 protozoon or a protoph^'ton resemblances must be sought 

 between it and other organisms already classified. The 

 decision is based on a preponderance of resemblances. There 

 is no one characteristic which is decisive. There are today 

 a number of organisms classified by botanists as plants and 

 by zoologists as animals because there does not seem to be 

 sufficient evidence for a definite decision. Euglena, myxo- 

 mycetes or mycetozoa, spirochetes, are illustrations. 



Resemblances must be sought not alone in morphology, the 

 form of the cell, how it looks under the microscope. The 

 physiology of the organism must be compared, especially 

 the method of reproduction and the metabolism. Chemical 

 composition is fundamental in metabolism and this must be 

 studied. 



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