THE SPINAL CORD.—GENERAL. 487 
THE SPINAL CoRD AS A CONDUCTOR OF IMPULSES. 
Before considering the results arrived at in this connection, 
some brief account of the methods applied in the investigation 
of the subject is called for, to enable the student to appreciate 
their difficulties and possible fallacies, as well as such grounds 
of certainty as there may be for the conclusions reached. 
Three or four methods of research have been employed: 1. 
Sections of the spinal cord of varying extent, both unilateral 
and bilateral. In estimating the value to be attached to the 
symptoms following, the difficulties in limiting the section, the 
interference of hemorrhage, the inevitable results of operative 
shock, and, as in-all experiments on the nervous system of ani- 
mals, the danger of misinterpreting the symptoms, must be 
given due weight. 2. Attempts have been made to determine 
the course and relations of nerve-fibers by ascertaining the 
order in which the different portions of the spinal nerve-fibers 
receive their investing myelin, those with the longest course 
being the latest to be thus completed. “This is the method of 
Flechsig, who has mapped out the cord into a series of columns, 
to be referred to again presently. The method is open to the 
objection of all anatomical ones. It is a remarkable fact that, 
by strictly physiological methods (i.e., ascertaining the function 
of parts), nervous tracts have been traced, which were quite 
unsuspected as the result of anatomical investigation alone. 
Nevertheless, this method, taken with others now under con- 
sideration, has rendered important service. 3. Following upon 
experimental sections, as well as in consequence of certain dis- 
eases in the brain and cord, fibers have been found to degenerate 
along certain definite paths, owing, it is believed, to being cut 
off from their trophic centers; so that if, after section of the 
cord, there is degeneration of fibers downward, it is inferred 
that the trophic cells lie above the seat of degeneration and 
the reverse. This may be called the pathological (Wallerian) 
method, and in conjunction with clinical evidence has, in the 
case of man especially, been the chief source, perhaps, of our 
knowledge in regard to the conducting paths in the human 
cord; though other methods, as carried out in the lower ani- 
mals, have yielded results which have been supplementary and 
corrective; and in truth a variety of means must be employed, 
and the greatest caution observed, or the inferences drawn will 
be partial if not actually erroneous. 
It is to be carefully borne in mind now, and when studying 
