34O PHYSIOLOGICAL CHEMISTRY. 



Inosite occasionally occurs in the urine in albuminuria, diabetes 

 mellitus and diabetes insipidus. It is claimed also that copious 

 water-drinking causes this substance to appear in the urine. Inosite 

 was at one time considered to be a sugar but is now known to be 

 hexahydroxybenzene, as the formula on p. 339 indicates. It is an 

 example of a non-carbohydrate in whose molecule the H and O 

 are present in the proportion to form water. In other words it has 

 the formula of the hexoses, i. e., C 6 H 12 O 6 . Inosite occurs widely 

 distributed in the vegetable kingdom and because of this fact the 

 theory has been voiced that it represents one of the first stages in the 

 conversion of a carbohydrate into the benzene ring. It is found in 

 the liver, spleen, lungs, brain, kidneys, suprarenal capsules, muscles, 

 leucocytes, testes and urine under normal conditions. 



EXPERIMENT. 



i. Detection of Inosite. Acidify the urine with concentrated 

 nitric acid and evaporate nearly to dryness. Add a few drops of 

 ammonium hydroxide and a little calcium chloride solution to the 

 moist residue and evaporate the mixture to dryness. In the pres- 

 ence of inosite (o.ooi gram) a bright red color is obtained. 



LAIOSE. 



This substance is occasionally found in the urine in severe cases 

 of diabetes mellitus. By some investigators laiose is classed with 

 the sugars. It resembles laevulose in that it has the property of 

 reducing certain metallic oxides and is Isevorotatory, but differs 

 from laevulose in being amorphous, non-fermentable and in not pos- 

 sessing a sweet taste. 



MELANINS. 



These pigments never occur normally in the urine but are present 

 under certain pathological conditions, their presence being especially 

 associated with melanotic tumors. Ordinarily the freshly passed 

 urine is clear, but upon exposure to the air the color deepens and 

 may at the last be very dark brown or black in color. The pig- 

 ment is probably present in the form of a chromogen or melanogen 

 and upon coming in contact with the air oxidation occurs, causing 

 the transformation of the melanogen into melanin and consequently 

 the darkening of the urine. 



