io Biological Chemistry. 



is known as metabolism, the building-up process, or forma- 

 tion of a complex from simpler substances, being described 

 as one of anabolism, and the reverse or degrading process 

 as one of katabolism. Where these proceed in a normal 

 manner, the organism is stated to be acting physiologi- 

 cally ; but where deviations from the norm occur, a patho- 

 logical condition results, which may lead to a well-marked 

 disease or even the death of the organism. A knowledge 

 of biological chemistry is therefore essential for a satis- 

 factory study of the functions of the organism, and the 

 modern physiologist has endeavoured not only to elucidate 

 the chemical changes produced on living objects as a whole, 

 but also to ascertain the particular organs which are con- 

 cerned in any given chemical change. 



In addition to the carbon (organic) compounds, animal 

 or vegetable bodies contain also certain amounts of mineral 

 matter, the presence of which can be demonstrated when 

 the organisms are burnt. When the combustion is com- 

 plete, the carbon is oxidized to carbon dioxide, and the 

 hydrogen to water, and the presence of the inorganic 

 matter is then revealed by the fact that a residue of in- 

 combustible mineral matter (" ash ") always remains. Part 

 of this forms an essential constituent of certain tissues ; 

 thus, bones contain calcium phosphate, the red-blood cor- 

 puscles of animals contain iron, and the green chloroplasts 

 of plants contain magnesium, and the iron and magnesium 

 in the two latter cases are found in a state of stable com- 

 bination with carbon compounds, and both elements are 

 essential for the normal development of the organisms 

 which contain them. 



Apart, however, from the mineral matter which forms 

 an essential constituent of the tissues, the bodies of plants 

 and animals contain certain quantities of salts, which do 

 not appear to enter into any form of combination with 



