March 15, 1883} 
NARORLE 
467 
ON THE NATURE OF INHIBITION, AND THE 
ACTION OF DRUGS UPON IT? 
Ill. 
oe first important contribution to our knowledge of 
inhibitory centres in the brain and spinal cord was 
that of Setchenow. He found that when the cerebral lobes 
in a frog were removed, voluntary motion was abolished, but 
reflex action became somewhat more marked. On removal 
of the optic lobes, the reflex action became very greatly 
increased, and if, instead of removing them they were 
stimulated either chemically by a grain of salt laid upon 
them, or electrically, reflex action in the limbs was greatly 
retarded or completely abolished. 
These experiments were repeated by Herzen, who, like 
Setchenow, considered that there was no inhibitory me- 
chanism in the spinal cord itself, but disbelieved also in 
inhibitory centres in the brain. He explained the depression 
of reflex which occurred on irritation of the optic lobes 
by supposing that any intense nervous irritation, no 
matter whether it was central or peripheral, caused great 
depression of reflex action both when the brain was intact 
and when it was divided, as in Setchenow’s experiments. 
Setchenow again repeated his experiments, and came to 
the conclusion that it was uncertain whether the inhi- 
bitory mechanism could be excited reflexly from the 
periphery. He made, also,a sharp distinction between 
tactile and painful impressions upon the skin. For 
tactile impressions he considered that there was no 
inhibitory mechanism in the brain. Further investiga- 
tions still, showed that both chemical and electrical irrita- 
tion would excite the inhibitory apparatus, and he, there- 
fore, considered that both excito-motor and depressor 
fibres were present in the same nerve-trunk.? Goltz found, 
in opposition to Setchenow, that there was an inhibitory 
apparatus for tactile reflexes also in the frog’s brain, 
but this he found in the cerebral lobes,? while Setchenow 
denied any inhibitory function to that part of the brain 
altogether. 
He found also, however, like Herzen, that complete 
abolition of reflex action could be produced by powerful 
irritation of any peripheral sensory nerve, and considers 
that the irritation is conveyed to the reflex centre, and 
diminishes or destroys its excitability for the original 
stimulus, without supposing that there is any special 
inhibitory centre. 
Lewisson found that by powerfully compressing the 
neck, or by squeezing the feet, or some other part of the 
body of a frog, or by irritation of the cutaneous or mus- 
cular nerves, or by electricity, the reflex excitability could 
be much depressed. He found, however, that unless the 
irritation was strong it produced stimulation both of the 
reflex and motor centres of the brain instead of de- 
pression.+ 
The general conclusion to which all these experi- 
ments, as well as those of Fick,® Freusberg, and others 
lead is, either that the nerves contain both excito-motor 
and reflex depressing fibres, or that excitement and 
depression can be produced by the same nerves under 
different conditions. 
Freusberg,® who discusses the question of inhibition in 
an able and thorough manner, comes to the conclusion 
that all instances of inhibition including the different 
effects of weak and powerful stimuli applied to the same 
nerve, and also the inhibitory effects of stimulation of 
different nerves on each other, are not due to specific 
* Continued from p. 439. 
Uber, die elektr. und chem. Reizung der sensiblen Ruckenmarksnerven 
des Frosches, 1868. Quoted by v. Boetticher, of. cif. p. 6. 
3 Goltz, of. cit. p. 42. 
4 Lewisson, ae Ueber Hemmung der Thatigkeit der motor. Nervencentren 
durch Reizung sensibler Nerven,’’ Archiv. f. Anatomie u. Physiol. 1869. 
5 Fick, Verhandlungen der physikalisch medicinischen Gesellschaft zu 
Wurzburg, April 23, 1870. 
© Freusberg, ‘‘ Ueber die Erregung u. Hemmung d. Thatigkeit d. 
nervisen Centralorgane,’’ Pfliiger’s Archiy. x. 174. 
inhibitory centres, but to a remarkable property of the 
central nervous system, which does not allow of its 
different parts being simultaneously set in action by 
different causes. This conclusion, although it may be 
nearer the truth than the hypothesis of separate inhi- 
bitory centres, is not satisfactory, for it still leaves us in 
the dark regarding the way in which the central nervous 
system comes to possess the remarkable properties which 
he attributes to it. 
Setchenow explains the increased rapidity of reflex 
action after section of the cord below the medulla 
oblongata, by supposing that there are two paths along 
which the stimulus usually passes, from the sensory to 
the motor tracts. The one goes directly across, and 
this is the path taken after section. The other goes up 
to the medulla, and then down the cord. This is the 
path taken under ordinary conditions; but besides the 
apparent unlikelihood that the stimulus should take this 
longer path under normal conditions, an objection has 
been raised to it by Cyon which seems fatal. 
Cyon finds that when the so-called inhibitory centres 
are stimulated, although reflex contraction of the leg is 
apparently delayed for a long time, this delay is to a great 
extent only apparent and not real. 
It is true that the vigorous contraction of the muscles 
which suffices to raise the limb is much delayed, but a 
contraction of these muscles commences at very nearly 
the same time that it would do if the inhibitory appa- 
ratus were not stimulated. This shortening of the muscle 
goes on very gradually for a considerable time, and then 
culminates in a sudden vigorous contraction, the total 
height of which is greater than that of the contraction 
wbich would have occurred without irritation of the 
inhibitory centres. It is very difficult to explain this 
result on the ordinary hypothesis, but easy enough on that 
of interference. According to it we suppose that a stimulus 
applied to the foot has been transmitted as usual from the 
sensory to the motor cells of the cord, and thence to the 
muscles, so as to initiate contraction in them. This stimu- 
lus would correspond to the first half wave in the diagram 
(Fig. 2). The subsequent waves of stimulation which 
would have proceeded from the motor ganglia have been 
interfered with by the stimuli passing down from the so- 
called inhibitory centre, but their times being not arranged 
so that each wave from the brain should fall half a wave- 
length behind that in the cord, the stimuli at length cease 
to interfere, and the contraction, which has gone on 
gradually increasing as the interference diminishes, at 
last finishes abruptly. ; 
The part of the brain which ought to correspond in 
higher animals to the optic lobes in frogs is the corpora 
quadrigemina, but irritation of these parts has not been 
found to have any marked inhibitory action upon reflexes 
in the limbs.? 
Irritation of the frontal lobes in puppies has, however, 
been found by Simonoff% to exercise an inhibitory action ; 
but, according to Ferrier, abolition of the frontal lobes in 
monkeys does not produce any very obvious effect upon the 
animal.? We know that by an effort of the will, we are able 
either to increase or diminish reflex action, and it might 
appear probable that irritation of the motor tracts in the 
cerebrum might have an inhibitory action on reflexes, 
Irritation of the cerebral motor areas has not been found to 
exercise any definite inhibitory action upon reflexes, but on 
the other hand Exner® has found, if a stimulus be applied 
simultaneously to a motor area in the brain and to an 
extremity, the two stimuli aid one another, and produce 
a greater effect than they would separately. As irritation 
T Cyon, Ludwig's Festgabe, p. clxviii. 7 
2 Setschenow Physiologische Studien iiber die Hemmungs-mechanismen 
fiir die Reflexthatigkeit des Riickenmarkes im Gehirn des Frosches, p. 3 
(Berlin: Hirschwald, 1863). 
3 Simonoff, Arch. f. Anat. u. Phys. p. 545, 1866. 
4 Ferrier, Functions of the Brain, p. 230 (London, 1876), 
5 Exner, Pfliiger’s Archiv. xxviii. 487. 
