I860.] of the Vital to t?ie Physical Forces. 207 



into the domain of Life. The phenomena that seem altogether peculiar 

 to living bodies are now ranked in the category of vital actions ; they 

 are regarded as the results of a special form of force, which is as dis- 

 tinct from chemical affinity or from mechanical power, as these are 

 from each other ; and the scientific physiologist aims to discover the 

 laws of its operation, just as the chemist seeks for the laws of affinity, 

 or the physicist for those of motion. 



Now, of all forms of vital action, there is none so universal, so 

 fundamental, or so characteristic, as that by which the living organism 

 is built up — or rather builds itself up — from the germ, by the appro- 

 priation of materials derived from external sources, and subsequently 

 maintains itself in its typical form during its term of life ; and the 

 force which effects this has been commonly designated by some distinc- 

 tive title, such as the nisus formativus, the hildungstrieb, or the germ- 

 force. This force has been commonly considered to be originally 

 inherent in the germ, and to have been derived, like the material sub- 

 stance of that germ, from the parental organism which produced it. 

 In this mode of viewing the subject, all the organizing force required to 

 build up an oak or a palm, an elephant or a whale, must be concen- 

 trated in a minute particle, only discernible by microscopic aid ; and 

 the aggregate of all the germ-forces appertaining to the descendants, 

 however numerous, of a common parentage, must have existed 

 in their progenitor. Thus, in the case of the successive viviparous 

 broods of Aphides^ a germ-force capable of organizing a mass of living 

 structure, which would amount (it has been calculated) in the tenth 

 brood to the bulk of 500 millions of stout men, must have been shut 

 up in the single individual, weighing perhaps the l-lOOOth of a grain, 

 from which the first brood was evolved. A more complete reductio ad 

 ahsurdum 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, ah externa^ during the whole period 

 of the exercise of its activity. 



When we carefully look into the question, we find that what the 

 germ really supplies is not the force, but the directive agency ; thus 

 rather resembling the control exercised 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 agency of the germ may be regarded, like 

 Magnetism, as a static force ; and just as magnetism requires to be 

 combined with motion to enable it to develope electricity, so does the 

 directive agency of the germ need the co-operation of a dynamic 

 force for the manifestation of its organizing power. That dynamic 

 force, as we learn from an extensive survey of the phenomena of 

 life, is 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 physiologists, who, however, 

 have only recognised in it a vital stimulus^ calling forth the latent 

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



