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structure, if we examine that which comes from the highest organism, 
and that which is concerned in the formation of the lowest, no diflference 
whatever can be distinguished. It is not that one is more complicated, or 
exhibits a structure different from the other. There is no structure in either. 
Both are perfectly clear, transparent, and structureless, and yet one is con- 
cerned in the performance of certain functions and offices, while the other is 
concerned in the performance of totally different functions and offices. Are 
we, then, to believe that the difference in the functions discharged is due 
merely to the chemical properties of the substances of which the living matter 
is composed? We cannot do this, because, when we come to analyse the 
two different kinds of living matter, we find in the material which results 
from their death the same elements. And, if the elements are not in pre- 
cisely the same amounts or in the same proportions to one another, the 
difference wffiich may exist in the composition bears no relation and has no 
reference that can be discovered, either to the difference in action or to the 
different structures which may be evolved from the two different forms of 
living matter. Therefore the terms “ simplicity ” and “ complexity ” seem 
to me to be totally inadmissible, and I venture to think that not one 
of those who are in the habit of speaking of simple and complex forms can 
give a rational explanation of what he means by the phrases he employs. 
What is generally meant by the simplest form of living matter is that when 
it attains its highest form of development it is still a simple thing, and what 
seems to be understood by that of the greatest complexity is, that when 
it attains its highest degree of development certain marvellous structures 
are produced ; but when we come to look at the living matter itself there is 
no difference to be discerned by any means of examination yet adopted 
between the two forms. The living matter, which, at the very earliest 
period of his development, represents man, is, as far as I know, not dis- 
tinguishable from the forms of living matter of which the simple bodies 
Dr. Wallich has so lucidly described to us are made up. And, therefore, 
the difference cannot be chemical. Neither can it be called physical, nor 
mechanical, nor can it be due to difference in machinery or mechanism, for 
none is to be discovered. The difference is enormous, and it is of a most 
remarkable kind, but it is not to be explained by any facts in physical science 
with which we are acquainted. All we know is, that under certain conditions 
one form of living matter grows and produces a certain kind of structure, 
and that under different conditions certain other forms of living matter grow 
and produce a structure that is totally different. The difference between the 
two is not in molecular or chemical constitution. They do not remarkably 
differ in chemical composition, and we may safely say it is impossible thus 
to explain the difference. That is the whole of the matter ; the difference in 
the results cannot be explained by physics or chemistry, and I do not think 
it ever will be so explained. The difference is one which can only be spoken 
of under another term altogether, and this is a word to which many object 
very strongly. I allude to the word “ vital.” The difference in question is a 
vital difference, dependent not on a property which belongs to matter itself 
