294 WHAT IS LIFE 



in space of certain groups), structural isomerism, 

 dynamic isomerism (tautomerism) , etc. See Tau- 

 tomerism. 



Isotopes. The name, proposed by Soddy, for all 

 elements that are inseparable by chemical processes. 

 Isotopes have identical chemical properties, and the 

 same valency. They differ in atomic weight by small 

 amounts. The radioactive isotopes always differ in 

 radioactive properties. 



Karyokinesis. Indirect cell-division. Also the 

 series of changes exhibited by the nucleus in such 

 cell-division. 



Kinetic Theory of Gases. The kinetic theory 

 teaches that each individual molecule of a gas is 

 endowed with motion, the velocity of which is 

 different for the different molecules (different ele- 

 ments), and which varies with the temperature. The 

 kinetic theory of gases is the theory according to 

 which all the phenomena exhibited by gases are 

 accounted for by the motion of their constituent 

 molecules. 



Kinetic Energy. The energy that belongs to a 

 body in motion. See Energy and Quantum. 



Metabolism. A general term that comprises both 

 anabolism and cataholism, and designates the changes 

 undergone by the food taken into the animal body. 

 In the limited sense of chemistry it means the proc- 

 ess of the building up of more complex substances 

 from simple substances (anabolism), or the breaking 

 down of complex substances into simpler ones (catab- 

 olism). In the wider view of biology it means the 

 process of the change of the food constituents into 

 living matter (anabolism), or the process bj'' which 

 living matter is broken down into simpler products 

 within a cell or an organism (catabolism). 



Metal. Chem. Any element that forms a base 



