NATURE OF VITALITY. 39 



is the " Ether, which, diffused throughout all nature, produces 

 in plants the bud, the secretion and motion of the juices, and 

 is separated from the blood and lodged in the brain of an- 

 imals." 



5. A fifth hypothesis, first proposed by Aristotle, was re- 

 vived by Stahl, and refers the phenomena of life to an ani- 

 mal soul, or immaterial principle wholly distinct from a soul, as 

 the responsible and intelligent part of man's nature. This 

 theory has been adopted by many, but it is evidently inappli- 

 cable to plants. This objection appears to be fatal to its truth, 

 although the Physical School, as those have been called who 

 adopted this theory, are mainly right in this, that in ascribing 

 the functions of life to a soul, " they mark strongly and justly 

 the impossibility of ascribing them to any known attributes 

 of body."* 



Various attempts have also been made to define life, or to 

 analyze the idea of it. 



1. The most correct definition of life is given by Bichat, 

 and modified by Whewell. " Life is the system of vital func- 

 tions" These functions are of two kinds, those which per- 

 tain to organic life, which are the same both in animals and 

 vegetables, and those which belong to animal life, which in- 

 clude sensation and voluntary motion. 



2. Some suppose that the idea of life is simple, and hence 

 the effects of it are explained by reference to a single prin- 

 ciple. 



3. Others attempt to separate life into a series of vital func- 

 tions, such as secretion, assimilation, absorption, etc. and 

 hence muke the idea of it complex. 



But in all these attempts, there seems to be a necessity of 

 referring the phenomena of life to some distinct force. This 

 force has been variously denominated organic attraction or 

 vital attraction, organic affinity or vitcd affinity. Professor 



* See Whewell's Philosophy of Inductive Sciences, Vol. II, in 

 which these and other hypotheses are examined. 



