THE CELL 31 



theory, which states that all living bodies are built of cells, just 

 as a honeycomb is built of chambers formed by partitions of wax. 

 During the World War, some one discovered that not the Ger- 

 mans but a Frenchman, Dutrochet, had first formulated the 

 cell theory, and then, as is so often true, when the matter was 

 looked into, it was found that six other scientists had simultane- 

 ously and independently propounded the same theory in one 

 form or another, but the credit is still usually given to Schleiden 

 and Schwann. Indeed, if we are to observe the rule of priority, 

 we must go back to the ancients, for it was Aristotle who, in a 

 sense, first advanced the cell theory, even though he had never 

 seen a cell. He used in its place the hypothetical term "ele- 

 ments." In his "Historia Animalium," he writes "of the parts 

 of animals some of which are 'simple' (elements or cells) and 

 others 'composite'" (tissues). Later, he carried this idea still 

 further when he wrote of "elements," "parts uniform with 

 themselves," and "parts not uniform with themselves," that is 

 to say, cells, tissues, and organs. He undoubtedly did not 

 think of the cell as we know it today, but he had the concept 

 of the organism built of units. The chief facts brought out by 

 the cell theory are that all organisms are built of structural units 

 essentially alike, and that these units, or cells, are themselves 

 complete living entities. 



This last concept led to the faulty idea that cells in tissues 

 are isolated units. Cells when acting as parts of larger bodies 

 do not live and function wholly independently of each other. 

 It is not enough for a cell to go on living its own independent 

 life; it has its duty to other cells and to the organism as a whole, 

 just as has a citizen to the state. No collective whole, be it a 

 community, a machine, or an organism, can function unless its 

 structural units are coordinated. Each cell influences and is 

 itself influenced by the activities of every other cell in the organ- 

 ism. Equally important to this interrelationship between cells 

 within the body is the influence of the extracellular environment. 

 Cells are bathed in body fluids. It was the great French physi- 

 ologist Claude Bernard who emphasized the importance of the 

 inner environment of the cell. 



The question arises whether the body fluids are alone sufficient 

 to maintain a coordinated activity between cells. Is not some 

 living connection between cells necessary? In animals, the 



