202 ZOOLOGICAL PHILOSOPHY 



cause of vital movements, from which arises the action of the fluid 

 on the organs and the reaction of the organs on the fluids. It is then 

 purely from the relations between these three objects that the move- 

 ments, changes, and all the phenomena of life result. 



In order to improve the comparison between a watch and a living 

 body we should have to compare the exciting cause of organic move- 

 ments with the spring of the watch, and regard the supple containing 

 parts, together with the essential contained fluids, as the machinery 

 of the movement in question. 



It will then be clear, in the first place, that the spring (exciting cause), 

 is the essential motive power, without which the whole remains in- 

 active, and that its variations of tension must be the cause of the 

 variations of energy and rapidity of movements. 



In the second place, it will be obvious that the machinery of move- 

 ment (the organs and essential fluids) must be in a state and arrange- 

 ment suitable for the performance of the movements which it has to 

 carry out ; hence, when this machinery gets out of order the effective 

 power of the spring is lost. 



From this point of view the parallel is complete ; a living body 

 may be compared with a watch ; and I can easily show the close 

 accuracy of this comparison by reference to known facts and observa- 

 tions. 



As to the machinery of movement, its existence and faculties are 

 now well known, as also most of the laws which control its various 

 functions. 



But as to the spring, the essential motive power and originator 

 of all movements and activities, it has hitherto escaped the researches 

 of observers : I beheve, however, that I shall be able to describe it in 

 the next chapter, in such a way that it cannot in future be neglected. 



But first let us continue the enquiry as to what essentially con- 

 stitutes life. 



Seeing that life in a body results exclusively from the relations 

 existing between the containing parts in an appropriate condition, 

 the contained fluids moving in them, and the exciting cause of the 

 movements, activities and reactions which take place, we may include 

 what essentially constitutes life in the following definition. 



Life, in the 'parts of any body which possesses it, is an order and state 

 of things which permit of organic movements ; and these movements 

 constituting active life result from the action of a stimulating cause which 

 excites them. 



This definition of life, either active or suspended, includes all the 

 positive facts which have to be expressed in it, and covers all special 

 cases. It appears to me impossible to add or subtract a single word 



