108 CHEMICAL COMPOSITION OF ANIMAL TISSUES. 



168. Albumen exists, not merely in the white and yolk of the egg, 

 but also in the various liquids which supply the materials for the nutri- 

 tion of the Animal tissues. Thus it is found in the Chyme, or product 

 of the digestive operation, whenever Animal flesh, or any Vegetable 

 substance corresponding with it in composition, has been taken in as 

 food. And it is absorbed from the alimentary canal into the Chyle 

 and Blood, of whose solid constituents it forms a very large proportion. 

 In its soluble state, Albumen is always combined with a small quantity 

 of free soda, with which it seems to be united as an acid with its base ; 

 and to this state of combination, its solubility is regarded by most 

 Chemists as being due. When the fluid in which it is dissolved is eva- 

 porated at a low temperature (not exceeding 126), the Albumen, or 

 rather Albuminate of Soda, may be dried, without losing its solubility ; 

 when dried, it may be exposed to a temperature of 212, without under- 

 going change ; and it forms, when again dissolved in water, the same 

 glairy, colourless, and nearly tasteless fluid as before. . When a higher 

 temperature is employed, however, the Albumen passes into the insolu- 

 ble form ; and presents itself either as a cloudy or flocculent precipitate, 

 or as a firm consistent coagulum, according to the strength of the origi- 

 nal solution. The same condition regulates the amount of heat requisite 

 for the purpose ; thus if the quantity of albumen be so great that the 

 liquid has a slimy aspect, a temperature of 145 or 150 is sufficient for 

 the purpose, and the whole becomes solid, white, and opaque; but in a 

 very dilute condition, boiling is required, and the albumen then sepa- 

 rates in the form of white finely-divided flocks. In either case the soda 

 and other soluble salts are separated from the albumen, and remain 

 dissolved in the water. When the coagulation of Albumen takes place 

 rapidly, the coherent mass seems quite homogeneous, and shows no trace 

 of anything like definite arrangement ; but when the process is more 

 gradual, minute granules present themselves, which do not, however, 

 exhibit a tendency towards any higher form of -structure. The insolu- 

 ble coagulum, or pure Albumen, dries up to a yellow, transparent, 

 horny substance ; which, when macerated in water, resumes its former 

 whiteness and opacity. Pure Albumen may also be obtained from the 

 solid mass which remains when an albuminous fluid is dried at a low 

 temperature, by reducing it to a fine powder, and then washing it with 

 cold water on a filter ; common salt, with sulphate, phosphate, and car- 

 bonate of soda, are dissolved out ; and a soft swollen mass remains upon 

 the filter, which has all the characters of Albumen obtained by precipi- 

 tation, except that it is readily soluble in a solution of nitrate of potash, 

 which will not dissolve the latter substance. 



169. Albumen may be thrown down from its solution, in a coagulated 

 state, not merely by heat, but by Alcohol and Creasote, and by most 

 Acids when added in excess, so as to do more than neutralize the alkali. 

 Nitric acid is particularly efficacious in occasioning its coagulation ; on 

 the other hand, Hydrochloric and Acetic acids, and common or tribasic 

 Phosphoric acid, do not precipitate it, these acids having the property 

 of dissolving pure Albumen. When albumen is dissolved in hydrochlo- 

 ric acid, a pinkish hue is at first seen ; the liquid then becomes of an 

 intense purple colour, and, on applying heat a little longer, an intense 



