84 PRINCIPLES OF PHYSIOLOGY 



hydrates. When oxidized, as by burning, they 

 are resolved into carbonic acid and water, 

 with a great evolution of heat. The chief fats 

 are tri-stearin, tri-palmitin, and tri-olein. 

 When a fat is acted on by lipase (an enzyme), 

 it hydrolyses and splits into a fatty acid and 

 glycerine. If a fat is acted on by an alkali 

 a soap is formed and glycerine is liberated. 

 42. Along with proteins, carbo-hydrates, and 

 fats, there are various salts, such as chloride of 

 sodium (common salt), chloride of potassium, 

 various phosphates of soda, potash, lime, and 

 magnesia. In the ash of organic matters we 

 also find sulphur and iron compounds, but these 

 are derived not from inorganic compounds 

 of these elements, but from decomposition of 

 the proteins It is doubtful if any of these 

 inorganic salts exist during life in a free state ; 

 it is more than probable that they are usually 

 combined with organic bodies, and that in 

 this way they take their part in vital pheno- 

 mena. The proportions of the various salts, 

 as determined by chemical analysis, is very 

 uncertain. It may be that certain saline 

 matters are simply dissolved in the colloidal 



