CARBOHYDRATES 91 



Fats are insoluble in water and in cold alcohol; soluble in hot alcohol, 

 ether, and chloroform. Colorless and tasteless ; easily decomposed cr saponi- 

 fied by alkalies or superheated steam into glycerin and the fatty acids. 



Certain of the monatomic Fatty Acids are found in the body, 

 viz., Formic CH 2 O 2 , acetic C 2 H 4 O 2 , and propionic C 3 H 3 O 3 , present in sweat, 

 but normally in no other human secretion. They have been found else- 

 where in diseased conditions. Butyric acid, C 4 H 8 O 2 , is found in milk and 

 in sweat. Various others of these acids have been obtained from blood, 

 muscular juice, feces, and urine. 



Of the diatomic fatty acids, one acid, Lactic acid, C 3 H 6 O 3 , exists in a 

 free state in muscle-plasma, and is increased in quantity by muscular con- 

 traction, but is never contained in healthy blood. 



Soaps. The fatty acids in combination with soda or potash, 

 or similar bases, form soaps which are soluble in water, while the fats are 

 not soluble. 



CARBOHYDRATES. 



The carbohydrates are bodies composed of C, H, and O, as aldehydes 

 and ketols. They are classified as monosaccharides, dextrose, galactose, 

 etc. These are the simplest molecules of the hexoses. They are sweet, 

 odorless, soluble in water, and oxidize readily, hence their reducing power. 

 They form crystalline osazones. They rotate polarized light. Their for- 

 mula is C 6 H 12 O 6 . Disaccharides, maltose, saccharose, lactose, etc. They 

 are formed by the union of two simpler molecules and the elimination of a 

 molecule of water. They have the formula C 12 H. 22 O n . And poly saccharifies, 

 glycogen, starch, dextrin, gum, etc. They are much less soluble, can be 

 hydrolyzed into the simpler forms, and have the formula (C 6 H 10 O 5 ) n . 



Monosaccharides are especially soluble and polysaccharides are espe- 

 cially insoluble; monosaccharides and disaccharides do not give colored 

 solutions with iodine, while polysaccharides do; monosaccharides and (ex- 

 cept saccharose) disaccharides reduce Fehling's solution, while polysaccha- 

 rides do not. 



Of these the most important are: 



Starch. It is contained in nearly all plants, and in many seeds, 

 roots, stems, and some fruits. It is a soft white powder composed of granules 

 having an organized structure, consisting of granulose .(soluble in water) 

 contained in a coat of cellulose (insoluble in water); the shape and size 

 of the granules vary according to the source whence the starch has been 

 obtained. It is not crystalline and will not dialyze. It is insoluble in cold 

 water, in alcohol, and in ether; it is soluble after boiling for some time, and 

 may be filtered, in consequence of the swelling up of the granulose, which 

 bursts the cellulose coat, and, becoming free, is entirely dissolved in water. 

 This solution is a solution of soluble starch or amydin. It gives a blue color- 



