134 PHYSIOLOGICAL AND PATHOLOGICAL CHEMISTRY. 



acid: the opalescence disappears owing to the conversion of 

 the glycogen into glycogen-dextrin and glucose. Neutralize 

 the cold mixture with sodium hydroxide or make it faintly 

 alkaline, add a few drops of Fehling's solution and heat : pre- 

 cipitation of red cuprous oxide. 



(e) Digest a few cubic centimeters of the glycogen solu- 

 tion with about 1 cc. of saliva at 40: in a very short time 

 the opalescence disappears and the solution no longer gives 

 the iodine reaction; if the digestion be continued one to two 

 hours the solution will give a marked reaction for sugar 

 (formation of maltose). 



(/) Add to a few cubic centimeters of the solution a drop 

 or two of lead acetate and then pass in hydrogen sulphide: 

 deep-black fluid, from which no lead sulphide separates and 

 which is not changed by filtering; glycogen, like gelatin, has 

 the property of holding fine precipitates in suspension, though 

 not to such an extent. 



II. DETECTION OF SUGAR. 



That part of the liver which was reserved for showing the 

 presence of sugar is kept for twenty-four hours and is then 

 chopped up. Heat it to boiling with ten times its weight of 

 water, adding a trace of acetic acid to precipitate the pro- 

 teids, filter, evaporate to about one-fifth of its volume, filter 

 again and use the solution for the reactions for the detection 

 of glucose (see chapter on Urine, page 117). Trommer's test, 

 the fermentation test, and the phenylhydrazine test are 

 sufficient. 



III. PREPARATION OF THE XANTHINE BASES. 

 Chop up finely 250 g. of beef- or calf's liver, put it into a 3.5 

 to 4 liter stoppered bottle with 2.5 liters of chloroform-water, 1 

 then add about 2.5 cc. more of chloroform, shake vigorously 



J Mode by shaking vigorously 2.5 liters of water with 12.5 cc. of chlo- 

 roform in a glass-stoppered bottle till the chloroform has dissolved. 



