OTHER MODES OF FORCE. 173 



nervous centres, the animal utters cries, and exhibits all the 

 indications of suffering pain, scarcely any muscular move- 

 ment being produced ; showing that in this case the nerves 

 of sensation are affected by the electric current, and therefore 

 that some definite polar condition exists, or is induced, in the 

 nerves, to which electricity is correlated, and that probably 

 this polar condition constitutes nervous agency. There are 

 other analogies given in the papers of M. Matteucci, and de- 

 rived from the action of the electrical organs of fishes, which 

 tend to corroborate and develope the same view. 



By an application of the doctrine of the Correlation of 

 Forces, Dr. Carpenter has shown how a difficulty arising 

 from the ordinary notions of the developement of an organised 

 being from its germ-cell may be lessened. It has been 

 thought by many physiologists that the nisus formativus, or 

 organising force of an animal or vegetable structure, lies dor- 

 mant in the primordial germ-cell. ' So that the organising 

 force required to build up an oak or a palm, an elephant or a 

 whale, is concentrated in a minute particle only discernible 

 by microscopic aid.' 



Certain other views of nearly equal difficulty have been 

 propounded. Dr. Carpenter suggests the probability of ex- 

 traneous forces, as heat, light, and chemical affinity, contin- 

 uously operating upon the material germ ; so that all that is 

 required in this is a structure capable of receiving, directing, 

 and converting these forces into those which tend to the assim- 

 ilation of extraneous matter and the definite developement of 

 the particular structure. In proof of this position he shows 

 how dependent the process of germ developement is upon the 

 presence and agency of external forces, particularly heat and 

 light, and how it is regulated by the measure of these forces 

 supplied to it. 



It certainly is far less difficult so to conceive the supply 

 of force yielded to organised beings in their gradual process 

 of growth, than to suppose a store of dormant or latent force 

 pent up in a microscopic monad. 



