166 DR ALISON’S OBSERVATIONS ON 
action, the cases in which it acts, and those in which it is unconcerned, are to a 
certain degree defined ;—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 the forces which belong to each organic element, depends, 
according to my judgment, the advancement of physiology.”* “ As the vital 
functions became better understood, 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 hy- 
per-mechanical and hyper-chemical.” “Tn 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 peculiar 
causes come into play; and next, to endeavour to obtain some insight into the 
peculiar character and attributes of these causes.” + 
When we say that the chemical changes which take place in living bodies 
are elucidated, we mean, of course, that they are referred to general laws, by 
which the phenomena observed in this department of Nature are found, by expe- 
rience, to be regulated. And when we say that these are laws of vitality or of 
vital action, we mean merely, that they are laws deduced from the observation 
of phenomena peculiar to the state of life,—taking for granted that it is always 
possible to describe, and practically to distinguish, those substances which we call 
living, from inorganic or dead matter; and that the only correct definition of 
vital principles or vital powers, is, that they are the laws or the powers which 
regulate the phenomena that are peculiar to the state of life. They are the gene- 
ral expression of the results of the observation, and generalization of the facts, 
which are observed in this department of nature, and which are ascertained to 
belong to this department alone. 
We are not, indeed, justified in asserting the existence of laws peculiar to 
the state of life, merely by the negative observation, that the phenomena referred 
to them are inexplicable by any known laws of inorganic or dead matter; we must 
have the positive observation that they are inconsistent with—that they take place 
* Hist. des Sciences Naturelles depuis 1789, p. 218. 
T Philosophy of the Inductive Sciences, vol. ii., pp. 39 and 47. 

