Dr Alison on the Principle of Vital Affinity, 133 



belief that a time would come, when discoveries in the che- 

 mical department of the science, — connecting the ingesta of 

 living bodies with the nourishment of their different textures, 

 and with the nature of the different excretions, — would elu- 

 cidate the chemical changes which are continually going on 

 in them, and are essential to their living state, as completely 

 as the discovery of the circulation of the blood illustrated 

 many of the conditions of the existence of living animals. It 

 appears to me that this anticipation has been more nearly 

 realized by recent chemical observations, than professed phy- 

 siologists have yet admitted ; — that not only the existence of 

 the principle of vital affinity has been established, but its 

 limits and mode of action, the cases in which it acts, and 

 those in which it is unconcerned, are to a certain degree de- 

 fined; — and that a short and general illustration of these 

 points may be of some advantage, if not to the progress of 

 the science, at least to the due appreciation, and proper 

 generalization and expression of the knowledge which has 

 been already acquired. 



To shew the importance of this inquiry, I need do no more 

 than quote a single sentence from Cuvier, with a statement 

 which is nearly a commentary upon it by Professor Whewell. 

 " It belongs to modern times to form a just classification of 

 the vital phenomena ; and upon the zeal and activity given to 

 the task of analysing ihe forces which belong to each organic 

 element, depends, according to my judgment, the advancement 

 of physiology."* *' As the vital functions became better un- 

 derstood, it was seen more and more clearly at what precise 

 points of the process it was necessary to assume a peculiar 

 vital energy, and what sort of properties this energy must 

 be conceived to possess. It was perceived when, and in what 

 manner and degree, mechanical and chemical agencies were 

 modified, overruled, or counteracted by agencies which must 

 be hyper-mechanical and hyper-chemicaV " In attempts to 

 obtain clear and scientific ideas of the vital forces, we have 

 first to seek to understand the cause of change and motion 

 in each function, so as to see at what points of the process 



* Hist, des Sciences Naturelles depuis 1789, p. 218. 



