CHEMICAL BASIS OF THE ANIMAL BODY. 1213 



When starch is treated with dilute boiling acids, the products 

 which have been so far described are formed in rapid succes- 

 sion, the whole being finally converted into dextrose. 



4. Animal-gum (C 12 H 20 O 10 + 2H 2 O) (?). 



This is described as a form of carbohydrate which may be 

 extracted by the prolonged action of superheated water from 

 salivary and mucous glands, and is found also in milk and 

 urine. It yields no coloration with iodine, is very feebly dex- 

 trorotatory and appears to form a compound with cupric oxide; 

 the latter is obtained when caustic soda and sulphate of copper 

 are added to its solution, and may be used for the separation of 

 animal-gum from urine. It is non-reducing, but yields a reduc- 

 ing sugar when boiled with mineral acids. 



5. Glycogen (C 6 H 10 5 ) W . 



This substance is from a purely chemical point of view ex- 

 tremely like starch, the similarity being most marked when the 

 hydrolytic products of the two are compared. A study of its 

 occurrence, behaviour and fate in the animal body leaves but 

 little doubt that it may be regarded from the physiological side 

 as truly the animal analogue of the vegetable starch, and as 

 such it is frequently spoken of as 'animal starch.' It was 

 first described as a constituent of the liver, and in more recent 

 times it has been found to occur in greater or less quantities in 

 many tissues of the adult body, as for instance the muscles, also 

 in white blood- and pus-corpuscles and other contractile proto- 

 plasm, in which its presence is significantly connected with 

 their specialized activity, not as an essential, as some have sup- 

 posed, but as a convenient accessory. It is also conspicuously 

 found in the tissues of the embryo before the liver is function- 

 ally active, and is present in large quantities in many molluscs, 

 as for instance the common oyster (9-5 p.c.). 



Preparation of glycogen. The liver of an animal (rabbit or 

 dog), previously fed with copious meals of carbohydrate, is 

 excised as rapidly as possible, cut into small pieces and thrown 

 into an excess of boiling water, at least 400 c.c. to each 100 gr. 

 of liver. After being boiled for a short time, the pieces are 

 removed, ground up as finely as possible in a mortar with sand 

 or powdered glass, returned to the original water and boiled 

 again for some time. On faintly acidulating the boiling mass 

 with acetic acid a large amount of the proteid matter in solu- 

 tion is coagulated and may be removed by filtration. The 

 filtrate is now rapidly cooled, and the proteids finally and com- 

 pletely precipitated by the alternating addition of hydrochloric 

 acid and of a solution of the double iodide of mercury and 



