100 THE MECHANICAL PUNCTIONS. 



Muscular contractility, of which there exists no trace in 

 the vegetable kingdom,* has been established by nature as 

 the primary moving power of the animal machine. This 

 agent is resorted to on all occasions where considerable me- 

 chanical force is wanted; just as in a great manufactory, 

 where an immense quantity of machinery is to be set in mo- 

 tion, and a great variety of work is to be executed, the hu- 

 man mechanist avails himself of some constant moving force, 

 such as that of water, or steam. The laws of inorganic mat- 

 ter furnish no power that could conveniently have been ap- 

 plied in the animal body for that purpose; but muscular 

 power, from its high intensity, is adequate to every object, 

 and has been accurately adjusted, by the most refined appli- 

 cation of the laws of mechanism, to all the degrees and kinds 

 of effects intended to be produced. 



Although the power be the same, yet the mode of its ap- 

 plication is exceedingly diversified; and the comparison of 

 these diversities is the more interesting, inasmuch as there 

 are few of the animal functions in which the ends to be an- 

 swered are so definite, and the operation of the expedients 

 employed is so plain and intelligible. For while the intri- 

 cate chemical processes of the living system generally elude 

 our research, and the higher faculties of sensation and per- 

 ception are dependent on still more recondite and mysteri- 

 ous powers of nature, the mechanical functions are effected 



scopic structure of the fibres of some of the involuntary muscles. See Ap- 

 pendix to his Translation of Edwards on the Influence of Physical Ag-ents in 

 Life, p. 443. 



* The principal instances, which have been adduced in support of the 

 opinion that muscularity occasionally exists in vegetable structures, are the 

 alternate movements of the leaflets of the Hedysarum gyrans, which have 

 been fancifully compared to the movements of the ribs in respiration; the 

 quick motions of the stamina of the Berberis, Opuntia, and many plants of 

 the genera Carduus, and Centaurea; the closing of the leaves of the Dionaea 

 muscipula; and the shrinking of those of the Mimosa pudica, or sensitive 

 plant. On a superficial view, it must be acknowledged that these motions 

 bear a resemblance to the effects of muscular contractility; but I believe 

 that naturalists are now generally agreed that there is no real analogy be- 

 tween these phenomena, and that there is no substantial evidence for tlie 

 existence of that property in the vegetable kingdom. 



