APP.] CHEMICAL BASIS OF THE ANIMAL BODY. 729 



When pure, dextrose is colourless and crystallises from its aqueous 

 solution in six-sided tables or prisms, often agglomerated into warty 

 lumps. The crystals will dissolve in their own weight of cold water, 

 requiring however some time for the process; they are very readily 

 soluble in hot water. Dextrose is somewhat sparingly soluble in alcohol, 

 and crystallises from anhydrous alcohol in prisms free from water of 

 crystallisation ; it is moreover insoluble in aether. 



The freshly prepared cold aqueous solution of the crystals possesses a dextro- 

 rotatory power of + 104 for yellow light. This, quickly on heating, more slowly on 

 standing, falls to + 56, at which point it remains constant. 



Dextrose readily forms compounds with acids and many salts ; the latter are very 

 unstable, decomposition rapidly ensuing on heating them. When its metallic com- 

 pounds are decomposed the decomposition is in many cases accompanied by the 

 precipitation of the metals, e.g. silver, gold, mercury, bismuth. Caustic alkalis 

 readily decompose them, as also does ammonia. 



Dextrose is readily and completely precipitated by lead acetate and 

 ammonia. 



An important property of this body is its power of undergoing fer- 

 mentations. Of these the two principal are : (1) Alcoholic. This is 

 produced in aqueous solutions of dextrose, under the influence of yeast. 

 The decomposition is the following : C 6 H 12 O 6 = 2 C 2 H 6 O + 2 CO^, 

 yielding (ethyl) alcohol and carbonic anhydride. Other alcohols of the 

 acetic series are found in traces, as also are glycerine, succinic acid and 

 probably many other bodies. The fermentation is most active at about 

 25C. Below 5C. or above 45C. it almost entirely ceases. If the 

 saccharine solution contains more than 1 5 per cent, of sugar it will not 

 all be decomposed, as excess of alcohol stops the reaction. (2) Lactic. 

 This occurs in the presence of decomposing nitrogenous matter, especially 

 of casein, and is probably the result of the action of a specific ferment 1 . 

 The first stage is the production of lactic acid, C 6 H ]0 O 6 = 2 C 3 H 6 O 3 . 

 In the second butyric acid is formed with evolution of hydrogen and 

 carbonic anhydride: 2 C 3 H 6 O 3 = C 4 H 8 O 2 + 2 CO 2 + 2 H 2 . The above 

 changes, the first of which is probably undergone by sugar to a consider- 

 able extent in the intestine, are most active at 35C. ; the presence of 

 alkaline carbonates is also favourable. It is moreover essential that the 

 lactic acid should be neutralized as fast as it is formed, otherwise the 

 presence of the free acid stops the process. 



The preparation, detection and estimation of dextrose are so fully 

 given in various books that they need not be detailed here. 



1 Lister, Path. Soc. Trans. Vol. for 1873, p. 425, also Quart. Jl. of Micros. 

 Science, Vol. xviu. (1878), p. 177. 



