OF VITAL ACTIONS IN GENERAL. 43 



to Vital activity, will be fully explained in the next Chapter ; and at 

 present it will be sufficient to remark, that the degree in which they are 

 supplied possesses a well-marked influence upon the amount of activity 

 and energy manifested in the actions of the organized structure ; that 

 there is a limitation in the case of each of them, as to the degree in 

 which it can operate beneficially, the limitation being usually narrower 

 and more precise, according to the elevation of the being in the scalar 

 that an excessive supply may be destructive to the vital properties of 

 the organism, by over-stimulating it, and thus causing it to live too fast, 

 or by more directly producing some physical or chemical change in its 

 condition ; and that a deficiency will keep down or suspend all vital 

 activity, leaving the structure to the unrestrained operation of those 

 agencies which are always tending to its disintegration, and consequently 

 occasioning a speedy loss of the vital properties, save in those cases 

 in which they may be preserved in a dormant condition, and which are 

 exceptions to the general rule, that the death or departure of the vital 

 properties follows closely upon the cessation of vital actions. 



49. Our fundamental idea of Life, then, is that of a state of constant 

 change or action ; this change being manifested in at least two sets of 

 operations; the continual withdrawal of certain elements from the 

 inorganic world ; and the incorporation of these with the peculiar struc- 

 tures termed organized, or the production from them of the germs that 

 are hereafter to accomplish this. As the conditions of this continual 

 change, we recognise the necessity of an organized structure on the one 

 hand, or of a germ which is capable of becoming so ; whilst we also per- 

 ceive the necessity of a supply of certain kinds of matter from the inor- 

 ganic world, capable of being combined into the materials of that struc- 

 ture, which may be designated as the alimentary substances ; and, fur- 

 ther, we see that the organism can exert no influence upon these, except 

 with the assistance of certain dynamical agencies, such as light, heat, 

 &c., that supply the forces or powers without which no change can occur. 

 And to these forces, acting under the conditions which the Organized 

 body alone can supply, may be attributed (as will hereafter appear) the 

 phenomena w T hich we distinguish as Vital. 



50. But just as we find among Inorganic bodies, that various kinds 

 are to be distinguished by their different properties, whilst all agree in 

 the general or essential properties of matter, so do we find that living 

 organized substances are distinguished by a variety of properties inherent 

 in themselves, whilst they all agree in the foregoing general or essential 

 characters. ^ In many instances, the difference of their properties is as 

 obviously coincident with differences in their structure and composition, 

 as it usually is among the bodies of the Mineral world : thus we find the 

 property of Contractility on the application of a stimulus, to be for the 

 most part restricted to a certain form of organized tissue, the Muscular; 

 and we find that the property by which that stimulus is capable of being 

 generated and conveyed to a distance, seems to be restricted to another 

 kind of tissue, the Nervous. In a great number of cases, however, very 

 obvious differences in properties manifest themselves, when no perceptible 

 variation^ exist, either in structure or composition; thus it would be 

 impossible to distinguish the germ-cell of a Zoophyte from that of Man, 



