CHAPTER VIII 



CONSTRUCTIVE AND DESTRUCTIVE METABOLISM 



SECTION 77. General. 



METABOLISM includes the whole of the chemical processes connected 

 with vital activity, which render it possible and which it at the same time 

 regulates and governs. The changes which the food-material may undergo 

 in metabolism are very numerous and varied, for in this way not only are 

 all the permanent or transitory formative materials obtained and various 

 reserve and other products formed, but at the same time certain katabolic 

 processes provide a supply of energy such as is essential for all vital activity. 

 The katabolic processes involved in respiration and fermentation render 

 kinetic energy available for various remarkable processes of synthesis 

 involving a production of substances with higher potential energy. Every 

 living cell exhibits unceasing katabolism and anabolism, and just as in 

 animals, a large part, and often almost the whole, of the organic food may 

 be utilized to provide energy (Sect. 50). 



The simplest cell must not only be capable of respiration, or of kata- 

 bolism in general, but must also be able to perform a variety of anabolic 

 processes, and frequently to produce proteids, cellulose and various carbo- 

 hydrates, organic acids, and many other compounds as well, either 

 simultaneously or successively. This may be accomplished when sugar 

 is the sole carbon-compound supplied, provided the requisite inorganic 

 salts are present, and this sugar can be obtained by fungi only from the 

 external world, whereas green plants manufacture their own. Metabolism 

 may cause most profound chemical changes and molecular reconstructions, 

 as is evidenced by the fact that certain fungi can grow equally well with 

 either methane or benzene derivatives as their sole source of organic food. 

 It follows that, in spite of the widely different chemical constitution of these 

 two groups of compounds, such a fungus is able to construct from either of 

 them all the substances it requires (cf. Sects. 50, 66). In such cases the 

 same end is reached from widely different points of departure, and this is 

 only possible by a series of changes, which may either follow one another in 

 the closest and most intimate sequence, or may be separated by intervals 

 of time or space. The food- material which is to undergo further change 



