THE CELL 



CHAPTER I 

 INTRODUCTION 



BOTH plants and animals, although they differ so widely in their 

 external appearance, are fundamentally similar in their anatomical 

 structure; for both are built up of similar elementary units, 

 which, as a rule, are only to be seen with the microscope. These 

 units, in consequence of a hypothesis which was once believed in, 

 but is now discarded, are called cells ; and the view that plants 

 and animals are built up in a similar manner of these extremely 

 minute particles is called the cell-theory. The cell-theory is 

 rightly considered to be one of the most important and funda- 

 mental theories of the whole science of modern biology. In tho 

 study of the cell, the botanist, the zoologist, the physiologist, and 

 the pathologist go hand in hand, if they wish to search into the 

 vital phenomena which take place during health and disease. 

 For it is in the cells, to which the anatomist reduces both plant 

 and animal organisms, that the vital functions are executed ; 

 they, as Virchow has expressed it, are the vital elementary units. 



Regarded from this point of view, all the vital processes of a 

 complex organism appear to be nothing but the highly-developed 

 result of the individual vital processes of its innumerable variously 

 functioning cells. The study of the processes of digestion, of the 

 changes in muscle and nerve cells, leads finally to the examination 

 of the functions of gland, muscle, ganglion, and brain. And just 

 as physiology has been found to be based upon the cell- theory, so 

 has the study of disease been transformed into a cellular pathology. 



Hence, in many respects, the cell-theory is the centre around which 

 the biological research of the present time revolves. 



Further, it forms the basis of the study of minute anatomy, 

 now more commonly called histology, which consists in the exami- 

 nation of the composition and minute structure of the organism. 



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