48 NATURE AND OBJECTS OF PHYSIOLOGICAL SCIENCE. 



red-hot, and is converted into an oxide. The minuteness of the division, 

 predisposing to chemical union, appears to be the occasion of our power 

 of causing many substances to combine, when one or both are in the 

 nascent state (that is, when just set free from some other combination), 

 which could not be made to unite in any more direct manner ; thus, when 

 a quantity, however minute, of any preparation of arsenic is dissolved 

 in fluid in which hydrogen is being generated, the hydrogen will detach 

 the metal from its previous combination, and will pass forth in union 

 with it, as arseniuretted hydrogen, a compound which cannot be formed 

 by the direct union of the elements. In like manner, in that mechanical 

 mixture of three finely-divided substances, which we call gunpowder, the 

 rapidity with which combustion is propagated through the largest col- 

 lection of it, is entirely dependent upon the minute subdivision of its 

 components, and the very close approximation of their particles. Hence 

 it may be very correctly said, that the true chemical properties of the 

 substances are not manifested, except when they are in a state of very 

 minute division ; and that these are in fact obscured, by the aggregation 

 of the particles into masses. Thus, then, we are at no loss to discover 

 examples, in the Inorganic world, of an alteration in the sensible pro- 

 perties, both Chemical and Physical, of the bodies composing it, by a 

 change in the conditions in which they are placed. And it may be 

 stated as a general fact, that we never witness the manifestation of new 

 properties in a substance, unless it has undergone some change in its 

 own condition, of which altered state these properties are the necessary 

 attendants. 



58. Now if we apply the same methods to the phenomena of Life, we 

 shall see that they will lead to a mode of viewing them, which will con- 

 siderably tend to the simplification of Physiological science. In the 

 first place we have to look at these phenomena as the results of certain 

 forces, acting through those forms of matter which we term Organized ; 

 and these forces we shall provisionally designate as Vital. Thus in the 

 growth of the simple Vegetable cell, as already described ( 26-41), 

 we trace the operation of a force closely allied to ordinary chemical 

 affinity, but so far different that it can only be exerted through a living 

 organism ; of a force of assimilation or vital transformation ; and of a 

 force of organization and complete vitalization. Now although we may 

 provisionally designate these as distinct forces, on account of the diver- 

 sity of their manifestations, it is impossible not to see that they are 

 mutually dependent, and that they form the successive elements of a 

 continuous series of phenomena belonging to the same category, that of 

 cell-life; and further, we observe that they operate under the same 

 conditions, namely, the presence of a cell-germ and of the materials of 

 its growth, and the action of light and heat. Again, in the multiplica- 

 tion of the original cell, by whatever method performed, we cannot but 

 trace the continued action of forces of the same character ; since this 

 operation takes place as a continuation of the process of growth, and 

 under precisely the same influences. Further, we occasionally meet 

 with examples, even among the simplest forms of Vegetation, of very 

 active movement ; thus the filaments or elongated cells of the Oscillato- 

 rice are continually bending themselves backwards and forwards, with a 



