80 THE CHEMICAL CONSTITUENTS OF THE BODY 



B. CHOLESTERIN 



Cholesterin is a monatomic alcohol, C 27 H 45 OH, which occurs' especially in 

 certain biliary concretions, also in the brain, in nerves and in animal cells gen- 

 erally. From an alcoholic solution it crystallizes in the form of leaflets which 

 have the appearance of mother-of-pearl. With the higher fatty acids cholesterin 

 forms esters, which, unlike the fats, are very resistant toward decomposing 

 reagents and are therefore specially suitable for protection to the skin, being 

 found on both hair and feathers. Lanolin, a compound of this kind prepared 

 from wool fat, has found wide practical use. 



C. CARBOHYDRATES 



The name carbohydrates is applied to substances composed of C, H, and 

 0, in which the H and are present in the proportions to form water. This 

 definition however is not sufficient, for there are substances with the same 

 relative quantities of H and which are not carbohydrates; and for other 

 reasons it cannot be regarded as satisfactory from a scientific point of view. 

 A perfectly satisfactory definition of carbohydrates has not yet been given; 

 they are characterized only as aldehyde or Tcetone derivatives of polyhydric 

 alcohols. 



The carbohydrates are divided into three chief groups, namely, monosac- 

 charides, disaccharides and polysaccharides, in each of which are found sev- 

 eral familiar substances. 



A. The monosaccharides are the direct, isomeric or stereo-isomeric alde- 

 hydes or ketones of the corresponding alcohols. They occur ready formed in 

 nature, and have also been prepared synthetically. 



The monosaccharides most interesting to us in this connection are the 

 hexoses, C 6 H 12 O : dextrose, mannose, galactose, and levulose, which are the first 

 oxidation products of the stereo-isomeric hexatomic alcohols: sorbite, raannite, 

 and dulcite. The latter have the following constitution: CH 2 .OH.(CH.OH) 4 . 

 CH 2 . OH. Dextrose, mannose, and galactose are the respective aldehydes of these 

 alcohols, CH 2 .OH.(CH.OH) 4 .CHO; levulose is the ketone of mannite, CH,. 

 OH.(CH.OH) S .CO.CH 2 OH. 



The following reactions are common for all these substances: They are 

 directly fermentable, and under the influence of the yeast plant are decom- 

 posed into CO 2 and alcohol: C 6 H 12 O 8 = 2C 2 H 6 . OH -f 2CO 2 . They are easily 

 oxidized and hence reduce the metallic oxides on heating in alkaline fluids. 

 This property is made use of in quantitative determinations of the monosaccha- 

 rides. They are for the most part crystalline substances of a sweetish taste; 

 readily soluble in water, difficultly soluble in alcohol. The hexoses occurring in 

 nature, in solutions rotate the plane of polarized light either to the right or to 

 the left. This property also is valuable for their quantitative determination. 



1. Dextrose (synonyms : grape sugar, glucose) occurs in sweet fruits (e. g., 

 grapes) and in honey. Under normal circumstances dextrose is found in small 

 quantities in the blood and lymph. In diabetes its quantity in these fluids is 

 greater, and it is found in large quantities in the urine. Dextrose rotates the 

 plane of polarized light to the right. 



2. Levulose (synonyms: fruit sugar, fructose) occurs together with dextrose 

 in sweet fruits and in honey. It rotates the plane of polarized light to the left. 



