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LETTERS TO A STUDENT. 
No. II. — The Errors of Inquiry. 
There are many kinds of erroneous investigation of which 
I can give no account. It would be well to have them described 
and arranged into classes ; but that is a task for which I am 
quite unfit, and it belongs not to a veterinarian. I merely mean 
to point out one or two of the most obvious causes of error. The 
first to which I would direct your attention is, that of taking 
something for granted before it has been examined. 
It is a general law of matter that one substance shall not 
operate upon another unless the two be placed in close approxi- 
mation : the space between must be so little that none shall be 
perceived. This fact is learned at a very early period of man’s 
existence. No one remembers how or when he was first aware 
of it, and few know that it is a piece of knowledge acquired by 
repeated observations. It is constantly in our possession, and no 
one heeds it ; yet all act as no one could act without it. I men- 
tion this law merely that I may tell you of a few exceptions to it. 
You have at all times, and unconsciously, spoken and thought 
as if you had considered it a universal law. It is only general. 
Among inanimate objects there are numerous and sublime 
examples of matter acting upon matter at a distance of infinite 
magnitude. There are others in which the distance is consider- 
able, but not great. Such is the case in the phenomena exhi- 
bited by the magnet. You will find ample illustration of this 
in any treatise on astronomy and natural philosophy. I need 
not waste time in proving that which has been so long known. 
Had all men been as familiar with the exceptions as with the 
general law, medical science would have had fewer errors than 
it now acknowledges. The examples of one substance acting 
upon another placed at a visible distance, are rare in the ordi- 
nary affairs of life. They are discovered only by systematic 
investigation. To ignorance of this fact may be traced many 
fruitless attempts to explain some vital phenomena, which may 
not, and to me certainly do not, appear to require any expla- 
nation, at least none such as that which is usually offered. 
In a short time your attention will be called to the nervous 
system. You will learn the anatomical relations of the brain 
and the nerves. You will be told that the physiology of these 
parts is involved in a good deal of mystery. You will find that 
sensation depends upon the nerves, and that it is lost by dividing 
the nerves, or otherwise interrupting their connexion with the 
brain. The sentient nerves, it is said, are acted upon by the 
foreign body with which they come in contact. The impression 
is transmitted to the brain — but how ? This is the point at 
