MOLECULAR FORCES. 169 



mena to mechanical conditions, cannot be fairly tested till the 

 existence of this new force has been proved ; but how can such 

 proof be adduced in reference to a force the simplest effects of 

 which are unknown to us, and which differs from other forces 

 merely by its disregard of all restrictions, and of the limits pre- 

 scribed by physicists to laws ? It may be briefly asserted that the 

 exclusion of physical agency affords no proof of a purely vital 

 force ; and yet there is no other means by which its existence can 

 be established. The physicist who rigidly follows the leading 

 maxims of his own science, must admit the possibility of a vital 

 force, although he may regard any proof of its existence as at 

 present impossible. 



The time has passed when the assumption of different vital 

 forces was supposed to afford sufficient explanation of all or any 

 alterations occurring in organised bodies, or when these same 

 forces were fancifully represented as the architects of the organism, 

 and the stewards of the vegetable and animal economy, providing 

 all things, providently warding off all noxious matters, removing 

 all that threatened evil, executing all useful things, and everywhere 

 active, keeping a watchful guardianship over the whole organism. 

 But physiologists still exist, who regard those phenomena in the 

 vital economy, which we are as yet unable to explain on physical 

 principles, as a proof of the existence of a specific vital force. 

 Let us once more briefly consider the grounds which make such 

 an assumption simply problematical. 



If the proposition be established that no organised body can 

 be formed from the fortuitous elements of inert matter, and if 

 organised bodies must originate in organised structures only, and 

 finally, if, without life, life could not be generated, the elaboration 

 of organised bodies must depend upon that which is organised 

 upon life, or vital force. Such a sequence as this proves the im- 

 possibility of obtaining an insight, from a physical point of view, 

 into the origin and development of organic matter. We must 

 admit that in the physical sciences generally we meet with certain 

 boundaries beyond which we are conscious that the human 

 intellect never can or will pass. Thus astronomy, the most per- 

 fect of all the physical sciences, will never succeed in explaining 

 how the planetary system, with its satellites, was first set in 

 motion, or what gave the first impulse to the eccentric orbits 

 of the comets which traverse our solar system. Notwithstanding 

 Laplace's theory, we are ignorant of the primary cause of the 

 formation of the earth ; we are firmly convinced that, at a definite 

 period of the earth's development, the seeds of all plants were 



