INORGANIC BODIES. 71 



Group VI. FATS. 



These bodies have the same elements in their composition, but 

 the hydrogen and oxygen have variable proportions not that 

 of water. Fats are found in large masses in some tissues, and 

 also as fine particles suspended in many of the fluids. The fat of 

 adipose tissue in man is a mixture of olein, palraitin, and stearin, 

 which are commonly spoken of as the neutral fats. 



The first is liquid, and the last two solid at normal temperatures, 

 and the varying consistence of the fat of different animals depends 

 upon the relative proportions of the more solid or liquid fats. 



Fats are soluble in ether and chloroform, but quite insoluble 

 in water. When agitated in water containing an albuminous 

 body, or an alkaline carbonate in solution, fluid fat is broken up 

 into small particles, which remain suspended in the liquid so as 

 to form an opaque milky emulsion. 



Chemically, they are regarded as ethers derived from the tri- 

 atomic alcohol glycerin, C 3 H 5 (OH) S , by replacing the hydrogen 

 atoms of the OH group by the oxidized radicals of the fatty acids ; 

 thus 



Glycerin + Palmitic acid = Tripalmitin + Water. 



C 3 H 5 (OH) 3 + 3(C 16 H 32 2 ) = C 3 H 5 3 (C 16 H 31 O) 3 + 3H 2 O. 



Under the influence of certain ferments they separate into glyce- 

 rin and the fatty acid, taking up the necessary elements of water. 



When the neutral fats are boiled with alkaline solutions they 

 are similarly decomposed, and uniting with the elements of water, 

 form glycerin and fatty acids. The glycerin is thus set free, but 

 the fatty acid combines with the alkaline metal to form a kind of 

 soluble soap. An insoluble soap may be obtained by substituting 

 lead or lime, etc., for the alkali. 



This splitting up of the neutral fats, stearin, palraitin, and olein 

 into sodium stearate, palmitate, or oleate goes on during digestion, 

 and is said to be useful in aiding the absorption of fatty matters. 



INOKGANIC BODIES. 



Water (H 2 O) is present in nearly all tissues in larger proportion 

 than any other compound, making up about 70 per cent, of the 



