REPORT ON ANIMAL PHYSIOLOGY. 107 



that ova belonging to species the most different, are all develop- 

 ed, according to their kinds, under similar external conditions, 

 and that ova of the same species are true to their kinds under 

 conditions which are not absolutely the same for any two indi- 

 viduals. If we call this power vitality with modern writers, or 

 the anima with Stahl, these words can teach us nothing physio- 

 logically, unless we ascertain the law by which it operates : how- 

 ever we may see that the final cause of its operation is plainly 

 in every case the production of those numerous bodies, definite 

 with respect to families, genera, and species, which it develops 

 for its own manifestations in each. Our eyes inform us that 

 these bodies arise by means of the assimilative process, and 

 that the original power exhibits its faculties by means of the 

 organs which it has produced through this process. Our idea 

 then of the vital power is this,— that it is connected with the 

 matter of the germ in the act of its formation, and resides in it 

 as the potential whole, or sufficient cause, of the entire future 

 organism ; that in consequence of the excitability of the or- 

 ganic matter of the germ, imparted to it in the same act of its 

 formation, the expansion of the germ into portions or members 

 occurs by the visible process of assimilation or nutrition, each 

 portion thus acquiring its own excitability and its own reactive 

 energy, which are but partial manifestations of the original 

 power ', and that in proportion as each part is developed, new 

 internal conditions are introduced, in consequence of the new 

 formation, which affect all that previously existed, by modifying 

 the assimilative process in all. The phases of this process are 

 strictly defined for each species, and the subsidiary means neces- 

 sary for the purposed effect — as in the various forms of the re- 

 spiratory organ in the foetal state of the same individual to mode- 

 rate the condition of external air — are amongst the most beau- 

 tiful instances of provision for a definite end. 



This formative act, this process of assimilation or nutrition, 

 which is thus performed by animals and plants, and lias a rela- 

 tion not only to the present, but the future also, appears to be 

 the determination of a power acting according to Reason ; and 

 hence it must have been that Stahl referred it to the rational soul. 

 But, seeing that reason cannot exist without consciousness, — 

 a faculty which manifests itself only by means of the brain, a 

 late product of this very power by the act of assimilatioji, — seeing 

 also that the effect may be modified, within limits, (as in cases 

 of monstrosity,) when the conditions are altered, we rather con- 

 clude with Harvey that it proceeds from a power acting accord- 

 ing to fixed laws. " Vegetativae operationes potius videntur 



