CHAPTER IX 

 ENZYMES 



THE TOOLS OF THE CELL 



" Instances of Magic ; .... By which I mean those wherein the material 

 or efficient cause is scanty and small as compared with the work or effect pro- 

 duced ; so that even when they are common, they seem like miracles, some at 

 first sight, others even after attentive consideration." BACON. 



THE living cell is a factory where, without any great display of 

 energy, work is carried on which, outside the body, could only be 

 done by the use of strenuous processes. In the cell are prepared 

 secretions which act on insoluble raw material, rendering it 

 soluble and so fit for transit to the cell and passage into it. Within 

 the cell, these prepared materials undergo further change ; some 

 are used as sources of energy ; from others, the cell builds up 

 complex tissue ; others again are altered somewhat and stored 

 for future use. The cell manufactures from the material supplied, 

 various substances such as are required, it may be by distant 

 cells which are so occupied by some special process that they are 

 unable to perform the particular synthesis. The by-products of 

 manufacture are rendered harmless by processes possible, as yet, 

 only in the cell. Some cells, as indicated above, have a specialised 

 function. To a certain extent, all the cells of a multicellular 

 organism are specialised. They are divided into communities, 

 each engaged on some special work and requiring special raw 

 material. Some of these communities, however, engage to a 

 certain extent in general manufacture. They are almost, though 

 not quite, self-supporting. The white cells of blood, for instance, 

 are really unicellular organisms. Other communities are almost 

 entirely dependent on imports for their sustenance. Nerve cells, 

 for example, form the means for intercommunication between 

 cell-communities. Their general metabolism is peculiar. 



Contrast the quiet, economical, and neat living-factories with 

 the places where things are made outside the body. Our manu- 



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