168 ZOOCHEMICAL PROCESSES. 



sufficiently taken into consideration in the explanation of vital 

 phenomena, the tendency of latter times has rather been to attach 

 undue importance to them. All things which did not admit of 

 being referred in a simple manner to known mechanical means, 

 were ascribed to vital force, which, although as yet unknown, 

 might, perhaps, serve as a guiding light to future generations in 

 their advance on the paths of physical inquiry. But it was for- 

 gotten that there are very many phenomena in inanimate nature 

 which must be explained by physical laws, and that we have very 

 slight knowledge of the laws of molecular motion. The many 

 cases, too, have been overlooked in which chemical phenomena 

 are opposed to all the ordinary laws of affinity, whilst the theore- 

 tical deficiencies of our highly vaunted science of chemistry have 

 not been thoroughly admitted, notwithstanding the want of success 

 which has attended all the attempts hitherto made to explain the 

 highest chemical principles in simple mathematical symbols, and 

 to calculate their results by simple formulae. 



When we consider the deficient state of our knowledge of 

 many physical laws, and the varying circumstances by which their 

 results are modified, we can hardly suppose that all the pheno- 

 mena of animal matter can at present be referred to mechanical 

 conditions, and we shall be compelled to admit that there are no 

 grounds on which we can establish an exclusive vital principle 

 by which the phenomena of life can be explained independently of 

 purely physical forces. Physical inquiry demands that our investi- 

 gations into the existence of a vital force should be preceded by a 

 complete separation of all phenomena which can be referred to 

 purely physical forces, from those which depend upon some force 

 peculiar to life. Physical knowledge is, however, quite inadequate 

 in its present state to afford proof of this nature, for which we 

 must await a more perfect development of this branch of science. 

 We are still ignorant of the relation borne by the obscure agency 

 of the nerves to electricity; and, notwithstanding the attention 

 that has been directed to the study of the phenomena of the 

 nervous system, the physiologist would scarcely venture to deter- 

 mine whether these phenomena admit of being referred to certain 

 physical relations, or whether we are compelled to assume the 

 existence of some specific nervous agent peculiar to animal life. 

 As, however, we are still unable to refer nervous actions and 

 certain other phenomena of animal life to simple physical laws, 

 we must leave the proof to those who, even in the present day, 

 regard as undoubted the existence of a nervous agent or vital 

 force. The correctness of the view which ascribes vital pheno- 



