342 PRACTICAL PHYSIOLOGY 



to the product reduction indicates cane sugar. The 

 original solution will also taste sweet. 



C. Negative, and no solution of cupric hydrate. Absence of 



monosaccharides and disaccharides. 

 2. Add Iodine Solution. 



(a) A blue colour which disappears on heating, and returns on 



cooling indicates starch. 



(b) A brown colour which disappears on heating and returns 



on cooling indicates dextrin or glycogen. Confirm for 

 polysaccharides by heating some of the original fluid 

 for about fifteen minutes with a mineral acid, and testing 

 for sugar in the hydrolysed fluid. 



To distinguish between Starch, Glycogen, and Dextrin. Shake 

 up some of the original powder with cold water and filter. By 

 this treatment glycogen and dextrin will dissolve, starch will 

 not. Wash the filter paper thoroughly with water, then add 

 a drop of iodine solution a blue stain indicates starch. Add 

 iodine solution to the filtrate -a red colour indicates dextrin 

 or glycogen ; if the former body be present the filtrate is clear, 

 opalescent if the latter. 



To distinguish between Dextrose, Maltose, and Lactose. 



(1) Prepare osazone crystals and examine under the micro- 



scope dextrosazone gives long thin needles ; malt os- 

 azone, short thick needles ; lactosazone, needles of 

 varying length and thickness. 



(2) Barfoed's reaction may also be tried. 



II. For Proteins. 



1. Apply the Biuret reaction (a) A violet colour indicates native 



proteins ; (6) a rose pink colour, proteose or peptone. 



2. Apply Millon's and the Xantho-proteic tests. 



(a) A well-marked reaction indicates ordinary proteins 



(b) A faint reaction (combined with a distinct Biuret, 



and the absence of coagulation on boiling) points to 

 gelatine. (Confirm by noting if the solution gelatinises 

 on cooling.) 



If the Biuret Test gives a Violet Coloration, 



A. Add a drop or so of dilute acetic acid and boil. A coagulum 



points to native proteins. To ascertain which of these 

 is present (i.e. albumin or globulin), half saturate some 

 of the solution with (NH 4 ) 2 SO 4 . A precipitate indicates 

 globulin ; filter ; if the filtrate still gives a coagulum 

 on boiling, albumin is present. 



B. Carefully neutralise some of the solution. A precipitate 



may be : 



1. Alkali Meta-protein 'Original^ the precipitate re- 



fluid alkaline (dissolves on adding 



2. Acid Meta-protein original (excess of acid or 



fluid acid J alkali. 



3. Nucleo-protein original fluid^ precipitate does not 



alkaline I disappear on adding 



4. Mucin original fluid alka- fa moderate excess 



line /of acid. 



