OTHER MODES OF FORCE. 157 



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, con- 

 tinuously 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 

 assimilation of extraneous matter and the definite develop- 

 ment of the particular structure. In proof of this position he 

 shows how dependent the process of germ development 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. 



As by the artificial structure of a voltaic battery, chemical 

 actions may be made to co-operate in a definite direction, so, 

 by the organism of a vegetable or animal, the mode of motion 

 which constitutes heat, light, &c. may, without extravagance, 

 be conceived to be appropriated and changed into the forces 

 which induce the absorption and assimilation of nutriment, 

 and into nervous agency and muscular power. Indications 

 of similar thoughts may be detected in the writings of 

 Liebig. 



Some difficulty in studying the correlations of vital with 

 inorganic physical forces arises from the effects of sensation 

 and consciousness, presenting a similar confusion to that 

 alluded to, when, in treating of heat, I ventured to suggest 

 that observers are too apt to confound the sensations with the 

 phenomena. Let us apply some of the considerations on 

 force, given in the introductory portion of this Essay, to cases 

 where vitality or consciousness intervenes. When a weight is 

 raised by the hand, there should, according to the doctrine of 

 non-creation of force, have been somewhere an expenditure 

 equivalent to the amount of gravitation overcome in raising 

 the weight. That there is expenditure we can prove, though 

 in the present state of science we cannot measure it. Thus, 

 prolong the effort, raise weights for an hour or two, the vital 



