766 General and Applied Biology 



(5) to ensure sufficiently long and frequent periods of rest for depolari- 

 zation purposes, and (6) to maintain the integrity of the poles of the 

 organism. 



In the light of the discussion above, there would appear to be greater 

 or lesser quantities of electricity in all animals. In the fishes of certain 

 species there are modified muscle cells which are arranged in series to 

 serve as electric organs. In such organs the electricity is produced, 

 stored, and discharged into the surrounding water for offensive and 

 defensive purposes. In these electric organs the positive pole of one cell 

 is arranged against the negative pole of the next, so that the voltage 

 produced is determined by the number of cells arranged in the series. 



Burdon-Sanderson in 1882 and Waller in 1913 demonstrated that such 

 motor plants as the sensitive plant and Venus's-fly trap display electric 

 variations during their specific response to stimuli. These electric action 

 currents are also known as "blaze" currents and are accompanied by a 

 temporary increase in the permeability of the plasma membranes of the 

 cells. Bose in 1907 stated that electrical phenomena attend the activi- 

 ties of plants. 



Enzymes 



An enzyme (Gr. enzymos, ferment) may be defined as a complex, 

 organic, catalytically active substance produced by living protoplasm, the 

 action of which is independent of the life processes of the protoplasm. 

 An enzyme is a chemical colloid, usually proteinlike, although the chemi- 

 cal formula has been determined for only a few of them. The numer- 

 ous enzymes act as catalyzers (activators) in chemical reactions but ap- 

 parently are not used up in the reactions. Enzymes play important roles 

 in the life processes of all cells, including the bacteria as well as the cells 

 of higher organisms. They were formerly called ferments which explains 

 their being named enzymes. Enzymes are usually named by adding the 

 suffix -ase to the name of the substance acted upon. For example, mal- 

 tase acts on maltose, lactase on lactose, and protease on proteins. The 

 total number of enzymes is as great as the number of different chemical 

 substances that are acted upon. The substance acted on by an enzyme 

 is called the substrate. The product formed by the action of the enzyme 

 on the substrate is unstable because the enzyme is released unchanged, to 

 be used over and over again. However, the amount of substrate which 

 may be affected is not infinite as is true of a catalyst. By doubling the 

 quantity of an enzyme, we reduce the time required for a reaction by 



