260 ZOOLOGICAL PHILOSOPHY 



their faculties, we may usefully adopt this method of distinguishing 

 the faculties common to all from those that are pecuhar to some. 



The faculties common to all hving bodies, — that is, the only faculties 

 that they have in common, are as follows : 



1. Feeding, by means of incorporating food substances ; the con- 

 tinual assimilation of a part of these substances ; lastly, the fixation 

 of the assimilated substances, which repair at first plentifully and after- 

 wards less completely the loss of substance which these bodies undergo 

 at all periods of their active hfe. 



2. Building up their bodies ; that is to say, forming for themselves 

 the substances of which they are made by means of materials which 

 only contain the principles of these substances, and which are mainly 

 supplied in the form of food. 



3. Developing and growing, up to a certain limit which varies 

 according to the species ; this growth being more than a mere aggrega- 

 tion of matter added externally. 



4. Lastly, reproducing themselves, that is producing other bodies 

 which are exactly like them. 



Whether a living body, animal or plant, has a very simple or very 

 complex organisation, whatever may be its class, order, etc., it 

 necessarily possesses the four faculties enumerated above. Now since 

 these faculties are the only ones common to all living bodies, they 

 may be regarded as constituting the essential phenomena presented 

 by these bodies. 



Let us now enquire how much we can ascertain with regard to nature's 

 methods for the production of these phenomena. 



If nature only creates life directly in bodies which did not previously 

 possess it ; if she only creates the simplest type of organisation (Chapter 

 VI.) ; lastly, if she only maintains organic movements by means of 

 an exciting cause of these movements (Chapter III.) ; we may ask 

 how the movements kept up in an organised body, can give rise to 

 the nutrition, growth and reproduction of that body, and at the 

 same time confer on it the faculty of forming its own substance 

 for itself. 



I have no desire to provide an explanation of all the details of this 

 wonderful work of nature ; for such an attempt would expose us to 

 the probability of error and might discredit the main truths yielded 

 by observation. I believe that the question propounded above is 

 sufficiently answered by the following observations and reflections : 



The activities of life, or the organic movements, necessarily produce 

 alterations of state both in the containing parts and in the contained 

 fluids of a living body, as a result of affinities and of the decomposition 

 of principles previously in combination : such decomposition being 



