26 LIFE AND DEATH. 



the nervous system; vital spirits governing most of 

 the other functions; and finally, natural spirits 

 regulating the liver and susceptible of incorporation 

 in the blood. In the sixteenth century, in the time of 

 Paracelsus, Galen's spirits became Olympic spirits. 

 They still presided over the functional activity of the 

 organs, the liver, heart, and brain, but they also 

 existed in all the bodies of nature. 



Van Helmont. Finally, the theory was laid down 

 by Van Helmont, physician, chemist, experimentalist, 

 and philosopher, endowed with a rare' and penetrating 

 intellect. Here we find many profound truths com- 

 bined with fantastic dreams. Refusing to admit the 

 direct action of an immaterial agent, such as the soul, 

 on inert matter, on the body, he filled up the abyss 

 which separated them by creating a whole hierarchy 

 of immaterial principles which played the part of 

 mediators and executive agents. At the head of this 

 hierarchy was placed the thinking and immortal soul ; 

 below was the sensitive and mortal soul, having for its 

 minister the principal archeus, the aura vitalis, a kind 

 of incorporeal agent, which is remarkably like the 

 vital principle, and which had its seat at the orifice of 

 the stomach. Below again were the subordinate 

 agents, the bias, or vulcans placed in each organ, and 

 intelligently directing its mechanism like skilful 

 workmen. 



These chimerical ideas are not, however, so far 

 astray as the theory of vital properties. When we 

 see a muscle contract, we say that this phenomenon 

 is due to a vital property i.e., a property without any 

 analogue in the physical world, namely contractility, 

 In the same way the nerve possesses two vital 

 properties, excitability and conductibility, \t\\\z\\ Vulpian 



