The essential features of all such catalytic actions are: (1) the velocity of the reaction is greatly altered, usually accelerated; (2) the catalytic agent does not appear as one of the initial substances, or end-products, of the reaction, and is not itself altered by the chemical change which is taking place; (3) the accelerating effect is directly proportional to the amount of the catalyst which is present; (4) relatively small amounts of the catalyst produce very large results in the reacting mixture; and (5) the catalysts cannot themselves initiate reactions, but only influence the velocity of reactions which would otherwise take place at a different rate (usually much more slowly) in the absence of any catalytic agent.
— from The Chemistry of Plant Life by Roscoe Wilfred Thatcher