.LIFE, ITS PHYSICAL BASIS AND SLMPLKST EXPRESSION 27 



plasmic stuff representing these two conditions must be disposed 

 in certain definite relations. Protoplasm must occur as a cell 

 or cells to be capable of performing the necessary activities of 

 life. Hence we must consider at the very beginning of any dis- 

 cussion of life the two things, protoplasm and the cell. 



The elements that compose protoplasm are the familiar ones, 

 carbon, nitrogen, hydrogen, oxygen, sulphur, phosphorus, 

 potassium, sodium, etc.; but these elements, or some of them, 

 are found in protoplasmic cells in certain complex combinations 

 which arc not found elsewhere in nature, and which therefore 

 actually and absolutely distinguish chemically living proto- 

 plasm from all lifeless matter. These particular combinations 

 are certain albuminous compounds or proteids, composed of 

 C, H, O, N, and S, and their complexity is extreme: the atoms 

 in a single molecule often number more than a thousand. The 

 molecules also are very large, which is probably the reason of 

 their characteristic nondiffusibility through animal membranes 

 or artificial parchment. 



In addition to these characteristic albuminous compounds 

 and various derivatives, of them, protoplasm usually contains 

 certain native albumins and certain other characteristic com- 

 pounds known as carbohydrates and fats (which differ essen- 

 tially from the albuminous substances in lacking nitrogen as a 

 composing element). There are also various salts and gases 

 and always water to be found in living substances. Water is 

 absolutely necessary to the physical condition of half fluidity 

 which gives to protoplasm its essential capacity for motion on 

 itself. The commoner salts found in living substances are 

 compounds of chlorine as well as the carbonates, sulphates, and 

 phosphates of the alkalies and alkali earths, especially common 

 salt (sodium chloride), potassium chloride, ammonium chloride, 

 and the carbonates, sulphides, and sulphates of sodium, potas- 

 sium, magnesium, ammonium, and calcium. The gases found 

 in living matter are oxygen and carbon dioxide. These, when 

 not in chemical combination, are almost always dissolved in 

 water, although rarely they may be in the form of gas bubbles. 



To sum up the relation of living matter to chemistry we may 

 say that life is always associated with protoplasm, and that this 

 protoplasm is made up of a few familiar inorganic elements, 

 particularly those of lowest atomic weight; that it does not 

 include any special so-called vital or life element, that is, any 



