PROPERTIES OF PROTOPLASM 9 



Chemically living matter may be summarized as con- 

 sisting of proteins, fats, carbohydrates and salts, the latter 

 playing some important part in the vital processes although 

 since they all do not appear in all types of protoplasm each 

 cannot be regarded as a sine qua non of living matter. The 

 absolutely essential elements are carbon, hydrogen, nitrogen, 

 oxygen, and phosphorus which enter into the composition of 

 pure nucleinic acid and which form the basis of all protoplasm. 



While chemical analysis gives an idea of the kinds of 

 elements entering into the composition of protoplasm after 

 death, it allows no conception of the numbers of chemical 

 bodies that are continually being formed during life, and 

 still less conception of the nature of the vital chemical proc- 

 esses. It is generally agreed that pure, ash-free proteids 

 are really inert and lifeless and that salts or electrolytes, 

 either organic or inorganic are necessary for the vital 

 processes. 



Chemical composition, therefore, does not carry us very 

 deeply into the mysteries of protoplasmic composition, nor 

 does it give any clue to the nature of the vital processes. 

 It shows, however, what chemical elements are essential for 

 continued life, i.e., what elements are necessary to provide 

 for in the food, for all living things are constantly using up 

 these substances in vital activities and replacing them from 

 the food materials selected from the environment. This dual 

 process of waste and repair, met with nowhere save in living 

 matter, is a second fundamental property of living things 

 and is generally spoken of under the heading metabolism. 



2. METABOLISM OR THE POWER OF WASTE AND REPAIR 



A very good idea of the effects of continued protoplasmic 

 activity in the absence of food may be obtained by keeping some 

 minute animal, for example a protozoon like Paramecium in a 

 sterile medium for a few days. Paramecium is a microscopic 

 water-dwelling animal to be found in any stagnant ditch or pond. 

 . Ordinarily it swims about actively by means of minute motile 



