14 INTRODUCTION. 
When condensed, this substance forms those lamin called 
membranes ; the membranes, rolled into cylinders, form those 
more or less ramified tubes named vessels; the filaments called 
Jibres are resolved into it, and bones are nothing but the same 
thing indurated by the accumulation of earthy particles. 
The cellular substance consists of a combination well known 
as gelatine, characterised by its solubility in boiling water, 
and forming, when cold, a trembling jelly. 
We have not yet been able to reduce the medullary matter 
to its organic molecules; to the naked eye, it appears like a 
sort of soft bouillie, consisting of excessively small globules; it 
is not susceptible of any apparent motion, but in it resides the 
admirable power of transmitting to the Me the impressions 
of the external senses, and conveying to the muscles the orders 
of the will. It constitutes the greater portion of the brain and 
the spinal marrow, and the nerves which are distributed to all 
the sentient organs are, essentially, mere fasciculi of its rami- 
fications. 
The fleshy or muscular fibre is a peculiar sort of filament, 
whose distinctive property, during life, is that of contracting 
when touched or struck, or when it experiences the action 
of the will through the medium of the nerve. 
The muscles, direct organs of voluntary motion, are mere 
bundles of fleshy fibres. All vessels and membranes which 
have any kind of compression to execute are armed with these 
fibres., They are always intimately connected with nervous 
threads, but those which belong to the purely vegetative func- 
tions contract, without the knowledge of the mr, so that, al- 
though the will is truly a means of ogi the fibres to act, 
it is neither general nor unique. 
The fleshy fibre has for its base a particular substance 
ealled fibrine, which is insoluble in boiling water, and which 
seems naturally to assume this filamentous disposition. 
The nutritive fluid or the blood, such as we find it in the 
vessels of the circulation, is not only mostly resolvable into the 
general elements of the animal body, carbon, hydrogen, oxygen 
and azote, but it also contains fibrine and gelatine, almost 
prepared to contract and to assume: the forms of imembranes , 
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