426 PRACTICAL PHYSIOLOGY 



B II. For the estimation of sugar, 1020 gr. of chopped-up liver are 

 pounded in a mortar with boiling water, faintly acidified with acetic 

 acid, and sand; boiled for a few minutes then filtered, neutralised,, 

 and the sugar estimated as on p. '274. 



A. The glycogen and sugar in the incubated liver are determined 

 by the same methods. 



It will be found that by standing at 36 C. much of the glycogen 

 disappears from the liver and that sugar increases. The liver possesses. 

 the power of hydrolysing glycogen even after death. It probably has. 

 a similar power during life. Immediately after death this hydrolysis, 

 of glycogen proceeds very rapidly, but can be much retarded by per- 

 fusing with iced water. 



CHAPTER III. 

 PROTEIDS. 



Chemical Nature. In order to construct the structural formula of 

 proteids it is necessary, first of all, to determine the exact nature of 

 their decomposition products. This has been done by decomposing 

 them, either by means of acids or alkalies, or by means of the ferment 

 trypsin. 



The isolation of the chief amido acids has already been given on 

 p. 227- The following method may be used for the separation of the 

 hexone bases (Kossel's method) and of glutaminic acid. 



A quantity of dried proteid is treated with three times its weight of con- 

 centrated hydrochloric acid, to which some stannous chloride is added to> 

 prevent oxidation. It is boiled with this for three days, the mouth of the 

 flask being connected with a Liebig's condenser so arranged that the condensed 

 vapour runs back into the flask. After this time the contents of the flask, 

 which are deep brown in colour, are removed, treated with H 2 S to remove 

 zinc, filtered, and evaporated to a syrup. This is placed on ice and in the 

 course of some hours large clear crystals of Glutaminic acid hydrochloridt 

 separate out. This is a di-basic amido acid having the formula: 



CH <COOH 

 CH< COOH 



and is closely allied to Aspartic acid (see p. 230). These crystals are separated 

 by filtration. The filtrate is then diluted with water and treated with a watery 

 solution of Phospho-tungstic acid. The resulting precipitate, which contains the 

 hexone bases, is then dissolved in boiling water, and treated with powdered 

 baryta in the heat till most of the ammonia gas has been evolved and all the 

 phospho-tungstic acid precipitated. The preparation is then filtered and CO^ 

 bubbled through the filtrate to precipitate the barium (as BaC0 3 ). The Ba-free 

 solution is again saturated with C0 2 , and mixed with a watery solution of 

 mercuric chloride till the reaction is acid. This treatment precipitates the 



