fiANDBOOK OF PHYSIOLOGY. 



by lead acetate, by silver nitrate, and by chlorine water. On boiling with 

 strong hydrochloric acid, it yields grape-sugar and certain nitrogenous 

 substances. Prolonged boiling in dilute acids, or in water, destroys its 

 power of forming a jelly on cooling. 



Keratin is obtained from hair, horns, fingernails, etc. Its composi- 

 tion is very similar to that of ordinary albumin and is approximately 

 C, 49.5, H, 6.5, N, 16.8, S, 4., 0, 23.2; the keratins obtained from the 

 various substances are distinct and differ slightly though closely related. 

 Sulphur is the characteristic body found in keratin and occurs as a sul- 

 phur-containing radicle ; a large amount of mercaptan sulphur can usually 

 be obtained. On decomposition, keratin yields argenin 2.26 per cent, 

 leucin 10 per cent, and tyrosin 4 per cent. 



Properties. Keratin is insoluble in water, salt, sodium carbonate, and 

 dilute hydrochloric acid ; is soluble slowly, when warmed, in caustic pot- 

 ash and sulphuric acid; gives Millon's and the xanthoproteic reactions. 



Neural era tin is a form of keratin which is found in the white sub- 

 stance of Schwann around the axis-cylinders of nerves. It yields arge- 

 nin 5 per cent, leucin 10 per cent, and tyrosin 3.5 per cent. 



Non-nitrogenous organic bodies consist of 



(a) Oils and Fats, which are for the most part mixtures of tri-pal- 

 mitin, C B1 H 9P B , tri-stearui C 67 H uo 6 , and tri-olein C 57 H 104 C , in different 

 proportions. They are formed by .the union of three molecules of fatty 

 acid with one molecule of the triatomic alcohol, glycerin C 3 H 5 (OH) 3 , and 

 are ethereal salts or esters of that alcohol. Palmitic acid is C 16 H 32 0,, ; 

 stearic acid is C lh H 3c 2 ; oleic acid is C ]b H 34 2 . Human fat consists of 

 a mixture of tri-palmitin, tri-stearin, and tri-olein, of which the two former 

 contribute three-quarters of the whole. Olein is the only liquid constitu- 

 ent. The fat of milk (and butter) is tri-butyrine ; butyric acid is C 4 ,H 8 ,0 2 . 



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

 ether, and chloroform. Colorless and tasteless ; easily decomposed or sa- 

 ponified by alkalies or super-heated steam into glycerin and the fatty acids. 



And (b) Carbohydrates, which are bodies composed of six or twelve 

 atoms of carbon with hydrogen and oxygen, the two latter elements being 

 in the proportion to form water. There are three main classes of carbo- 

 hydrates. 



Monosaccharides or Glucoses, C 6 H 12 6 , containing one molecule of su- 

 gar, and comprising Dextrose or Grape Sugar, Lsevulose or Fruit Sugar, 

 Inosite, etc. Disaccharides or Saccharoses, C 19 H M M , containing two 

 molecules of sugar from which one molecule of water has been with- 

 drawn, and comprising Saccharose or Cane Sugar, Lactose, Maltose, etc. 

 Polysaccharides or Amyloses, C 6 H J0 5 , containing a large but unknown 

 number of molecules of sugar from which water has been withdrawn, and 

 comprising Starch, Dextrin, Glycogeu, etc. 



