414 OF NUTRITION. 



animal,) we find that, putting aside the fatty matter of the yolk, albumen is the 

 sole organic compound, at the expense of which all its tissues are to be formed ; 

 so that, by the wonderful processes of chemical and vital transformation, which 

 take place during the period of incubation, the albumen which it contained at 

 first is metamorphosed into bone, cartilage, nerve, muscle, tendon, ligament, 

 membrane, areolar tissue, gelatinous matter, horny substance, feathers, &c., &c. 

 Secondly, a similar metamorphosis appears to be continually taking place in 

 the body of the adult animal; for every protein compound employed as food 

 appears to be reduced to the form of albumen in the digestive process ; so that 

 this becomes the essential constituent of whatever fluid is absorbed for the 

 nutrition of the tissues. It ,is true that gelatin taken in as food may be absorbed 

 and carried into the current of the circulation ; but there is no doubt that it is 

 incapable of being applied to the re-construction of any but the gelatinous 

 tissues ; and it seems questionable whether, even in these, it exists in a con- 

 dition that can rightly be termed organized. Moreover, as it is clear that the 

 gelatinous tissues may be formed at the expense of albumen, we are justified 

 in regarding this substance as the common pabulum for all. Hence albumen 

 seems to hold very much the same position in the animal economy, with gum 

 in the vegetable. As long, however, as albumen remains in the state regarded 

 by chemists as characteristic of it, it exhibits no tendency to become organized ; 

 and it is only when it has been subjected to certain peculiar vital influences, 

 and perhaps undergone a change in its chemical constitution, or, in other 

 words, has become converted into fibrin, that any such tendency manifests 

 itself. The properties of albumen may be studied in the white of egg, or in 

 the serum of blood, from both of which situations it may be obtained in a pure 

 state by very simple means. In the animal fluids it exists in a soluble state ; 

 and even when it has been dried (at a temperature of 126), it is readily dis- 

 solved again in water, forming a glairy, colourless, and nearly tasteless fluid. 

 In this condition it is always combined with a small quantity of free soda ; to 

 the separation of which (whether by the agency of heat or acids), its coagula- 

 tion is thought by many chemists to be due. On this view, pure albumen is 

 not soluble in water ; its solution being only accomplished by union with an 

 alkali. When dissolved in water it coagulates at 158 ; a very dilute solution, 

 however, does not become turbid until it is boiled. When the coagulation of 

 albumen takes place rapidly, a coherent mass is formed which shows no trace 

 whatever of organization ; but, when the process is more gradual, minute 

 granules present themselves, which do not, however, exhibit any tendency 

 towards a higher form of structure. It is thrown down from its solution, in a 

 coagulated state, by alcohol, creosote, and by most acids (particularly nitric) 

 with the exception of the acetic. These precipitates are definite compounds of 

 the acids with the albumen, which here acts the part of a base. On the other 

 hand, coagulated albumen dissolves in caustic alkalies, and neutralizes them ; 

 so that it must here act as an acid. A solution of albumen in water is precipi- 

 tated by acetate of lead, and by many other metallic solutions : and insoluble 

 compounds are formed, of which one the albuminate of the chloride of mer- 

 cury is of much interest, as being that which is produced by the mixture of 

 a solution of albumen with one of corrosive sublimate. Albumen, both in its 

 soluble and insoluble state, always contains a certain amount of sulphur ( 458), 

 which blackens metallic silver. Soluble albumen dissolves phosphate of lime ; 

 and about two per cent, of this salt may be separated from it in its coagulated 

 state. 



553. Subsequently to its introduction into the living system, Albumen under- 

 goes a very peculiar modification, by which it is converted into Fibrin. As 

 already mentioned ( 457) it appears from the analyses of Mulder and Scherer, 

 that the ultimate composition of these two substances is the same ; but their 



