No. 388.] MAINTENANCE OF THE EQUILIBRIUM. 457 
the arm — are relaxed ; thus the nerves of these muscles are 
stimulated, and there results a certain reflex contraction of these 
opposing muscles. An excess of the intended movement is 
thus prevented. If this opposition, this restraint, be for any 
reason lacking, the movement becomes disordered and unsteady, 
as we indeed see in certain diseases. 
Less striking, but yet not to be overlooked, is the réle which 
the so-called visceral sensations play in the process under con- 
sideration. From all the viscera there are nerves which convey 
sensations to the spinal cord and the brain ; of these sensations 
also we are, as a rule, unconscious, except when the organ from 
which they come is diseased. As soon as we become conscious 
that we have a liver, then the 
_ liver is usually diseased. The 
viscera are suspended freely 
within the body cavity; each 
change in the position of the 
body must then produce a 
greater or less displacement of 
the viscera. This displacement 
is not generally a matter of con- 
sciousness, yet an unconscious 
sensation is transmitted to the 
brain. It is evident, then, that 
the visceral sensations are of 
essential assistance in the pres- 
ervation of the equilibrium. Fic. 1.— Transverse section of spinal cord. 4, 
‘ ` + Burduch’s column; ca, anterior commissure; 
It will be in order td introduce © <s, anterior hora of gray matter; cof, postè- 
here a brief, anatomical note, Po rni g Comers iunda: gs, Coila co- 
We have thus far spoken of the pyramid tract; va,anterior root; 7A, posterior 
sense of touch, especially in aires ven 
the soles of the feet, and of sensations from the joints, tendons, 
muscles, and the viscera. These are all perceived by means of 
nerves which enter the spinal cord through the posterior roots 
(Fig. 1, 7%). If we examine a transverse section of the spinal 
cord (Fig. 1), we find about its center a reddish-gray mass (cop 
and coa), the gray matter, while the remainder of the section is 
made up of the white matter. This white matter consists 
