NATURE AND ORIGIN OF LIFE. 13 



metabolism. A building up or synthesis of substances 

 to form higher and higher compounds in the making of 

 which energy is absorbed this is the anabolic process ; 

 and a corresponding breaking down of these highest 

 compounds into simpler ones, and eventually into waste 

 products, during which energy is freed called the kata- 

 bolic process. In living substance there are, then, two 

 series of compounds : one leading up to the highest com- 

 plexity, and the other leading down to waste products 

 from which energy is no longer drawn. This mixture of 

 a double stream of substances undergoing these physico- 

 chemical changes is the living matter itself, the very 

 physical basis of life, known as protoplasm. 



In physical structure protoplasm is a viscid or semi- 

 liquid colourless substance ; seen under the highest 

 powers of the microscope it appears to be composed of 

 the minutest globules of a more liquid substance enclosed 

 in a meshwork of denser fluid. When dead protoplasm 

 is analysed it is found to be composed of a variety of 

 anabolic and katabolic proteins, associated with water 

 and certain mineral salts. Protoplasm is the essential 

 living substance present in all living organisms, the 

 seat of all their activities. There is no protoplasm apart 

 from life, and no life without protoplasm. 



Animals have lost the power of building up new proto- 

 plasm from inorganic matter, indeed from any compounds 

 lower than the simplest nitrogen-containing proteins or 

 their immediate derivatives (albumoses, peptones, ammo- 

 acids). They inevitably starve sooner or later on a diet 

 without protein, however much fat or carbohydrate it 

 may contain, since they are unable to replace the highest 

 nitrogen compounds which necessarily break down in 

 the metabolism of protoplasm. Speaking generally, 

 animals can build up the most elaborate proteins from 

 the simplest, and fats from proteins or simpler carbo- 

 hydrates ; but the carbohydrates themselves they are in- 

 capable of forming from inorganic matter. Thus although 



