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Scope of the problem 



General 



Many of the problems of life are transport problems. In the 

 first place how did a sufficient variety and concentration of mole- 

 cules get together to begin operations? Having solved this initial 

 problem, how does the organism capture additional molecules to 

 renew, energize, and replicate itself from an environment that may 

 become very dilute? How does it avoid solutes present in the en- 

 vironment (perhaps produced by itself) at more than optimal levels? 



Solutions to these problems obviously were reached. We can- 

 not doubt that a great deal of concentrating of protoplasmic com- 

 ponents takes place during life. If we permit, for example, a bac- 

 terial culture to autolyze, i.e., to hydrolyze its structure with its 

 own enzymes, we shall find produced very strong solutions of some 

 of the components that were originally drawn from a comparatively 

 dilute solution in the culture medium. Obviously, concentration has 

 occurred during assimilation, although we shall not find it profitable 

 to use the term transport in a sense broad enough to include all 

 events in assimilation. For our purposes, we shall limit transport 

 to the mode by which a solute passes from one phase to another, 

 appearing in the same state in both phases. 



As the scope of transport is considered more closely, its impor- 

 tance to the unsolved problems of biology is seen to be very great. 

 How does an organism carry out within itself so many chemical 

 reactions that are inherently incompatible? No chemist would try 



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