CHAPTER V. 



THE HYDROAROMATIC DERIVATIVES: THE CYCLOSES, 

 CHOLESTEROL AND CHOLIC ACID. 



GENERAL CHARACTERISTICS. 



A class of bodies here claims our consideration, the members of 

 which, while chemically distinct, are, in their physical behavior and 

 physiological properties intermediate in character between the carbo- 

 hydrates and the fats. At the one extremity we have the cy closes, 

 which although polyatomic alcohols, nevertheless resemble sugars in 

 their solubility in water, their percentage-composition which is repre- 

 sented by the formula CeH^Oe, and their decidedly sweet taste. At the 

 other we have cholesterol and the cholesterol esters or waxes which 

 resemble the fats in their insolubility in water and solubility in organic 

 solvents, and which are constantly associated with fats and fatty 

 substances in the tissues in which they occur. They all contain a 

 reduced benzole-ring and are thus related to the Terpenes; they are 

 furthermore hydroxy-derivatives and thus yield a variety of color- 

 reactions which depend upon the presence of a hydroxyl radical in the 

 benzole -ring. 



The extreme importance of these substances in the life of tissues has 

 only very recently come to be suspected, but the variety of parts they 

 are now known to play in essential activities of the living cell is so 

 extensive that we have come to regard them as constituting a very 

 significant factor indeed in the life-economy. Thus Inosite in combina- 

 tion with phosphoric acid is an important constituent of seeds and the 

 rapidly growing parts of plants, while in animal tissues inosite is found 

 in a variety of situations and forms an integral part of the molecule 

 of the active principle of the anterior lobe of the Pituitary Gland. 

 Cholesterol is found wherever fats occur in animal tissues, and the 

 remarkable effects which it exercises upon the growth of epithelial 

 tissues, 1 show that it plays an important physiological role. Choles- 

 terol esters or Waxes occur in abundance in vegetable tissues, while in 

 mammals they occur in noteworthy amounts in the fatty sheaths of 

 medullated nerves, and in the cortex of the Suprarenal Gland. Cholic 

 Acid, which is probably a derivative of cholesterol, occurs combined 

 with amino-acids (amino-acetic acid or ethyl amino-sulphonic acid) 

 in the bile, and the salts which these acids form with sodium, play an 

 essential part in accomplishing the digestion and assimilation of fats. 



1 Cf. Chapter xx. 



