324 THE AMERICAN NATURALIST. [Vot. XXXIII. 
We shall, then, find quite different causes for the occurrence 
of dizziness, according to the part of the balancing mechanism 
which has its functions destroyed. But first I must briefly men- 
tion a peculiar kind of dizziness which is not preceded by any 
injury to the nervous system, namely, physical dizziness. 
We must constantly remember that the process of equilibra- 
tion usually takes place unconsciously. But if we find ourselves 
upon a narrow plank lying across a brook, or on the edge of a 
precipice, we become conscious not only that we have a certain 
difficulty to overcome in order not to fall, but also that such a 
fall would be attended by very serious results to us. We at- 
tempt, therefore, by voluntarily exerting all our muscles, by 
extending the arms, and in other ways, to render the process of 
keeping our balance easier. But in reality we aggravate the 
difficulty and perhaps finally fall. Fear makes us especially 
clumsy. It is as if one were riding a beast of burden along a 
narrow mountain path. As is well known, in such a case one 
should give himself over to the animal, which is accustomed 
to travel safely ; but if the rider becomes afraid, and tries to 
guide the animal with the reins, it may easily happen that both 
perish together. In this figure the animal represents our un- 
conscious coérdination, which we destroy when we try con- 
sciously to assist it. 
If we return now to our diagram, it will essentially aid us in 
our study of the different kinds of dizziness. 
We will begin with the different varieties of sensation which 
participate in the maintenance of the equilibrium. In the 
disease of the spinal cord known as tabes dorsalis the posterior 
roots are first affected. The sensations from the muscles, 
tendons, and joints then become reduced or arrested. I notice 
that occasionally the tactile sensations of the skin do not suffer 
until late, or perhaps not at all; while, on the other hand, the 
destruction. of the visceral sensations is not rare. 
As a consequence of the loss of the muscular sense, a man 
afflicted with this disease shows peculiar symptoms. His 
motions are not regular, not properly gauged: in walking his 
feet go shuffling and bumping along, while if he sits they will 
cross ; again, one foot is lifted much too high in the air, though 
