PROPERTIES OF PROTOPLASM 9 



Chemically, living matter may be summarized as consist- 

 ing of proteins, fats, carbohydrates and salts, the latter play- 

 ing 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 form the basis of all protoplasm. 



While chemical analysis gives an idea of the kinds of ele- 

 ments 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 processes. 

 It is generally agreed that pure, ash-free proteins are really 

 inert and lifeless and that salts or electrolytes, either organic 

 or inorganic, are necessary for the vital activities. 



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 secondary 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 organs termed cilia and takes in as food still more minute 



