412 CORRELATION OF PHYSICAL AND VITAL FORCES. 



bodies of all the individual men that have lived from Adam 

 to the present day, must have been concentrated in the body 

 of their common ancestor. A more complete reductio ad ab- 

 surdum can scarcely be brought against any hypothesis ; and 

 we may consider it proved that in some way or other, fresh 

 organizing force is constantly being supplied from without 

 during the whole period of the exercise of its activity. 



When we look carefully into the question, however, we 

 find that what the germ really supplies is not the force, but 

 the directive agency ; thus rather resembling the control exer- 

 cised by the superintendent builder, who is charged with 

 working out the design of the architect, than the bodily force 

 of the workmen who labour under his guidance in the con- 

 struction of the fabric. The actual constructive force, as we 

 learn from an extensive survey of the phenomena of life, is 

 supplied by Heat, the influence of which upon the rate of 

 growth and development, both animal and vegetable, is so 

 marked as to have universally attracted the attention of Phys- 

 iologists, who, however, have for the most part only recognized 

 in it a vital stimulus that calls forth the latent power of the 

 germ, instead of looking upon it as itself furnishing the power 

 that does the work. It has been from the narrow limitation 

 of the area over which physiological research has been com- 

 monly prosecuted, that the intimacy of this relationship be- 

 tween Heat and the Organizing force has not sooner become 

 apparent. Whilst the vital phenomena of Warm-blooded ani- 

 mals, which possess within themselves the means of main- 

 taining a constant temperature, were made the sole, or at any 

 rate the chief objects of study, it was not likely that the in- 

 quirer would recognize the full influence of external heat in 

 accelerating, or of cold in retarding their functional activity. 

 It is only when the survey is extended to Cold-blooded ani- 

 mals and to Plants, that the immediate and direct relation be- 

 tween Heat and Vital Activity, as manifested in the rate of 

 growth and development, or of other changes peculiar to the 



