VITAL PROPERTIES OF THE TEXTURES. vii 



thickening of the liquid and its conversion into a jelly ; and in the jelly itself the 

 contraction still proceeds, causing separation of water, and division into a clot and 

 serum. Their permeability to fluids, their ready capability of physical changes, 

 and their comparative chemical inertness, are properties by which colloid bodies seem 

 fitted to form organised structures, and to take part in the processes of the living 

 economy. In a recent research,* Mr. Graham has found that silicic acid may 

 combine both in a dissolved and in a gelatinous state with a variety of very different 

 fluids without undergoing alteration ; and presuming that the organic colloids are 

 invested with similar wide powers of combination, he remarks that the capacity of a 

 mass of gelatinous silicic acid to assume alcohol, or even olein, without disintegration 

 or alteration of form, and to yield it up again in favour of some other substituted 

 fluid, may perhaps afford a clue to the penetration of the colloid matter of animal 

 membrane by fatty and other bodies insoluble in water ; and moreover, that the 

 existence of fluid compounds of silicic acid of a like nature, suggests the possibility of 

 the formation of a compound of colloid albumen with olein, soluble also and capable 

 of circulating with the blood. 



The important relation which this new chemical doctrine bears to the constitution 

 and organic processes of the animal body, has appeared to justify the introduction of 

 the present notice of it ; for further information the reader is referred to the sources 

 already cited. 



VITAL PROPERTIES OF THE TEXTURES. 



Of the phenomena exhibited by living bodies, there are many which, in 

 the present state of knowledge, cannot be referred to the operation of any 

 of the forces which manifest themselves in inorganic nature ; they are 

 therefore ascribed to certain powers, endowments, or properties, which so 

 far as known, are peculiar to living bodies, and are accordingly named 

 "vital properties." These vital properties are called into play by various 

 stimuli, external and internal, physical, chemical, and mental ; and the 

 assemblage of actions thence resulting has been designated by the term 

 "life." The words "life" and "vitality" are often also employed to 

 signify a single principle, force, or agent, which has been regarded as the 

 common source of all vital properties, and the common cause of all vital 

 actions. 



As ordinary physical forces, such as mechanical motion, heat, electricity, chemical 

 action, and the like, although differing from each other in specific character and mode 

 of operation, are nevertheless shown to be mutually convertible and equivalent, and 

 are held to be but different modifications of one and the same common force or 

 energy, so it may in like manner come to be shown that vital action is similarly 

 related to the physical forces as they are related to each other, and is also a mani- 

 festation, under conditions special to the living economy, of the same common 

 energy. 



1. Assimilative Force. Of the vital properties, there is one which is 

 universal in its existence among organised beings, namely, the property, 

 with which, all such beings are endowed, of converting into their own sub- 

 stance, or " assimilating," alimentary matter. The operation of this pover 

 is seen in the continual renovation of the materials of the body by nutri- 

 tion, and in the increase and extension of the organised substance, which 

 necessarily takes place in growth and reproduction ; it manifests itself, 

 moreover, in individual textures as well as in the entire organism. It has 

 been called the "assimilative force or property," " organising force," 



* On the Properties of Silicic Acid and other Analogous Colloidal Substances, Pro- 

 ceedings of the Royal Society, June 16th, 1864. 



