38 BIOLOGY OF PLANTS. 



combining these elements so as to reproduce them. The pro- 

 duction of woody fibre, gluten, starch, sugar, gum, resin, 

 vegetable oils, acids and alkalies, with a few exceptions, whol- 

 ly exceed the power of any known chemical or physical agent. 

 They can be accounted for only by supposing a new and pe- 

 culiar po\\^er inherent in the vegetable, which we call the pow- 

 er of life or the vital principle. 



Nature of vitality . Of this we are wholly ignorant. We 

 know it only from its effects. Like affinity and attraction, 

 it is an ultimate power, at least, so far as science is concerned ; 

 for aught we know it is the direct power of God exerted in 

 this particular way. 



Various hypotheses, however, have been suggested to ac- 

 count for the phenomena of life. A few of these may proper- 

 ly be introduced in this connection. 



1. Some, as Paracelsus, held to a spiritual being. The 

 business of digestion was performed by the demon Archaeus, 

 who had his abode in the stomach, and '' who, by means of 

 his alchemical processes, separates the nutritive from the 

 harmful parts of our food, and makes it capable of assimila- 

 tion. 



2. Others, as Silvius, conceived that the vital functions 

 were due to chemical agents, and that the power of life con- 

 sists in the action of acids and alkalies, in fermentation and the 

 like processes. 



3. A third class have proposed a mechanical hypothesis, 

 which originated about the time, and was the result of the 

 splendid discoveries of Galileo and Newton. The phenomena 

 of life were due to the form of the particles of matter, their 

 motions and mutual attractions. 



4. A fourth class suppose the existence of a vital jluid, up- 

 on which the peculiar functions of life depend. This hypo- 

 thesis was proposed by Frederic Hoffinan of Halle, 1()94. 

 The vital fluid was a material substance acting through the 

 nerves, and producing the actions of all the other organs. This 



