180 DR ALISON’S OBSERVATIONS ON 
immediately present themselves, first, How are the cells themselves formed (e. g. 
on the germinal membrane of the ovum) out of a matter which is originally with- 
out form, otherwise than by those very properties which are here ascribed to their 
existence? and, secondly, If the properties are dependent only on forms, why do 
they not exist in the dead state, when the forms are, in many instances, still per- 
fect? The enunciation of these questions seems to me sufficient to shew, that 
the correct expression of the state of our knowledge on this point is that already 
quoted from Lerpie, that the chemical forces in living bodies are subject, not 
simply to an influence of forms, but to “ the invisible cause by which the forms of 
organs are produced,” i. e., that we must include under the head of vital properties, 
both the mechanical, or simply attractive power, by which cells or other organs 
are formed out of amorphous matter, and likewise the chemical powers with 
which these cells are endowed. 
It is no objection to what has been stated, of the strictly vital nature of these 
chemical powers, to admit that their action is very often analogous to the principle 
to which the name catalysis is given by chemists, and which is exemplified likewise 
in the chemistry of inorganic compounds, where the combination of two sub- 
stances is determined by the presence of a third, which nevertheless takes no 
part in the combination itself; or that it is analogous to that disturbance of the 
equilibrum of chemical compounds, by which the fermentation of an organic com- 
pound is transferred to another in contact with it, although the changes in the 
two go on separately, and the compounds formed are different. It is quite true, 
that these modes of chemical action resemble and illustrate the manner in which 
living solids, themselves undergoing continual changes of composition, determine 
new arrangements of the elements of the compound fluids which are brought 
in contact with them. But this analogy is far from being an explanation or 
resolution of the one phenomenon into the other. In the first place, the analogy 
is essentially defective; because although it is true that in any living being, 
already existing, different chemical compounds already exist in different parts of 
the structure, which may act in these modes on the nourishing fluid, and deter- 
mine distinct transformations of these at different parts; yet this does not apply, 
as already observed, to the first formation of each of the textures, at its appro- 
priate point, from a homogeneous semi-fluid matter. But farther, although we 
were to admit the analogy of all the chemical processes going on in living beings, 
to these forms of simply chemical action, we should not thereby be authorised to 
conclude that the vital processes have not that peculiarity which makes it in- 
cumbent on us to regard them as a separate class. We say that the decomposi- 
tion of carbonic acid, the combination of the carbon with the elements of water 
to form starch, and the evolution of the oxygen, is a vital action,—not because it 
is a change different in kind from the decomposition of water and evolution of the 
hydrogen by iron and acid,—but simply because it indicates an affinity peculiar 
to the state of life ;—because in no other circumstances, when the elements of 

