INSTINCT AND REASON. Le 
principles dependent upon either mass or structure, whether 
alone or combined, 
But while the physiologist or the anatomist, with all the 
appliances of the scalpel and the microscope, searches out, 
we would almost say, all that can be learnt from these potent 
aids, he yet misses just that all-important element which sets 
the merely material machinery at work. If, as seems certain, 
the brain has a proper motion of a pulsating nature (which 
we should imagine to be highly consistent with natural 
analogies), it only confirms what we might have imagined 
a priort, viz., that the nerves are tubular vessels for the dis- 
tribution of a subtle fluid, or perhaps of more than one kind 
of subtle fluid, utterly undiscoverable by the scalpel; a fluid 
or fluids adapted for the instantaneous transmission of gan- 
elionie impulses, going from, and returning to, the cerebral 
cavities, like blood to and from the heart. 
We have suggested more than one subtle fluid, for while 
the blood is usually called the life of the animal, no one 
supposes that it is in any other sense the life than as the 
bearer of a prepared pabulum to every part of the organism, 
both for its building up, and for the supply of waste tissue. 
The real organic life is not hamal, but neural; not a gross 
fluid like the blood, but something which dominates the 
blood, as it does all the other particulars of the organism— 
something from which the blood itself derives its living 
properties. This subtle fluid must penetrate the whole body, 
through the agency of the nervous fibrilla, which are its con- 
ductors or transmitters. 
The material carrier or energiser of organic life must be of - 
a highly subtle character, and the term animal spirit may be 
applied to it. But no scientific test can be brought to bear 
directly upon it, though we may hope at some future {ime 
for side-hghts which may one day demonstrate its exist- 
ence. 
But, besides the animal spirit, or vehicle of organic life, 
the nervous centres must also be the material organs for the 
residence and expression of intellect and soul; and for these 
we can hardly conceive a fluid sufficiently subtle and 
ethereal. It need scarcely be said that these are sugges- 
tions, in which, however, it would be hard to say that there 
was anything unreasonable. Cerebral physiology, as, perhaps, 
the very highest walk of biology, is naturally in a very 
imperfect and undeveloped state, nor do we suppose that 
the most perfect and accomplished anatomist for a moment 
imagines that he has exhausted the subject, or even pene- 
