March 1, 1883] 
NATURE 
419 
at this theatre for about a year and a half without any 
accidents, and has proved to possess many advantages 
over gas as applied to the illumination of buildings of 
this description. Not the least amongst these are the total 
absence of heat and vitiated air in the house, and the 
length of time during which the decorations will retain 
their freshness and colour instead of becoming quickly 
faded and tarnished, as would be the case. were the old 
system of gas adopted. sf 
ON THE NATURE OF INHIBITION, AND THE 
ACTION OF DRUGS UPON IT 
BY inhibition we mean the arrest of the functions of a 
structure or organ, by the action upon it of another, 
while its power to execute those functions is still retained, 
and can be manifested as soon as the restraining power is 
removed. 
It is thus distinguished from paralysis, in which the 
function is abolished, and not merely restrained. 
Inhibition is cne of the most perplexing problems in 
physiology, and we have at present no satisfactory hypo- 
thesis regarding it. It plays, however, such a very im- 
portant part in pharmacology, that we cannot pass it 
over ; and as it is through the action of drugs upon the 
various functions of the body that we have already 
arrived at a knowledge of inhibitory actions, which would 
otherwise have been impossible—as, in fact, pharma- 
cology has here quite outstripped physiology—we are 
obliged to enter into some hypothetical considerations, in 
order to be able to form some kind of idea regarding the 
mode of action of many drugs. 
Hypotheses serve as “pegs on which to hang facts,” 
and by their aid the isolated facts which few memories 
could carry may be arranged, and their relation to each 
more readily perceived. A hypothesis serves also asa 
guide for further experiments, by which it may be either 
disproved or supported. Should facts be against it, so 
much the worse for the hypothesis ; it must be discarded, 
and another tried in its place; but if facts agree with it 
we obtain a means of predicting phenomena, and make 
another step in knowledge. Like other useful things, 
hypotheses are not without danger, and sometimes do 
harm by satisfying people and stopping further inquiry. 
Thus Sultzer noticed the peculiar taste produced by the 
contact of two dissimilar metals with each other and with 
the tongue forty years before Galvani; but at that time 
the doctrine of vibrations was employed to explain all 
natural phenomena, and he concluded that some pecu- 
liar vibration occurred frcm the contact of the metals, 
which produced the peculiar sensation on the tongue. All 
the world were satisfied with the explanation, and thus a 
prominent fact slept in obscurity from the time of Sultzer 
to that of Galvani, no further attempts being made to 
determine the nature of the vibrations or the laws which 
governed them.' Yet in their proper place hypotheses are 
most useful, and but for the hypothesis that light, heat, 
and sound are due to waves, our knowledge of their phe- 
nomena would be much less than it is. 
The cases of inhibition, as we may term them, which 
we meet with in the study of physics, are the production 
of complete silence by the interference of two sounds, 
and of darkness by the interference of two rays of light. 
When two sounds or two rays of light are combined, 
so that the crests of the waves of which they consist coin- 
cide, the sound becomes louder and the light brighter. If 
they are thrown together, so that the crests of the waves 
in the one sound or ray coincide with the sinuses or 
hollows of the other, they completely counteract each 
other, and silence or darkness is produced. 
When the waves are of different rhythms, the crests 
and hollows of the two sounds or rays, which at one time 
coincide, will gradually interfere, and again gradually 
* Ree’s Cyclopedia. Article ‘‘ Galvanism.” 
coincide, so that rhythmical alternations of loud sound 
and silence, of bright light and darkness, are produced. 
A good example of interference or physical inhibition, and 
one that affords an illustration well suited to our purpose, 
is that of Newton’s rings. When a lens of small curvature 
is placed on a plane surface of glass, a series of rings is 
observed, starting from the centre of the lens and passing 
concentrically outwards. If monochromatic light is used, 
such as pure yellow light, pure red light, &c., these rings 
are alternately bright and dark; but if white light is 
used, they appear as a number of circular bands of dif- 
ferent rainbow colours. The cause of these rings is, that 
though the surface of the lens appears to the eye to be in 
contact with the plate of glass over a considerable area, 
it is not really so; avery fine film of air of varying thick- 
ness being interposed between them. 
Fic. 1.—A very diagrammatic representation of interference in Newton’s 
rings. 
When a ray of light passes through the lens on to the 
glass, part of itis reflected back from the lower surface of 
the lens, and part of it from the upper surface of the glass 
plate. Between those two points there is a very minute 
film of air: one vay has therefore to travel somewhat 
Jurther than the other, The distance which it has to 
travel is only through the extremely thin layer of air lying 
between the surface of the lens and the glass and back 
again ; but this distance at some places is just sufficient 
to throw the waves in the one beam half a wave-length 
behind those in the other, and to produce darkness by 
their interference. 
As we recede from the point of most complete contact 
between the lens and the glass, the thickness of air in- 
creases, the ray has somewhat further to travel, and the 
distance is then just sufficient to throw it a whole wave- 
length behind the other ray ; no interference is produced, 
and we get a ring of bright light. 
Further outwards the increased thickness of the film of 
air is again sufficient to throw one ray a wave-length and 
a half behind its fellow ; interference is again produced, 
and darkness is the result. 
With rays, then, of one colour, or of one wave-length, 
we get alternately light and darkness by interference. 
But it is evident that the extra distance which the 
waves have to travel in order to produce interference will 
not be the same for long and short waves ; and thus it is 
found that when white light, which contains rays of diffe- 
rent wave-lengths, is used, the rings, instead of being 
alternately light and dark, are coloured. 
The very distance which was sufficient to throw the 
red rays half a wave-length behind the other, and to pro- 
duce interference, will throw, let us say, the violet rays a 
whole wave-length behind, and thus there will be no 
interference and vice versd; the distance which causes 
interference of the violet rays does not cause interference 
of the red, and so on with other colours. 
Thus the spaces which would have been perfectly dark 
when rays of pure red or pure violet, or more correctly 
ultra-violet, were used, would be filled up by the other if 
used together, and when white light is used, the various 
waves interfere at different places, and so we get a series 
of rainbow colours. 
The extra distance which one beam has to travel 
in order to produce interference with another is zot 
absolute, but relative to the wave-length, This relation 
differs for different wave-lengths, and therefore if the 
relative distances remain constant, the effect of the beams 
on each other will vary if their wave-lengths be changed. 
It is obvious that if both the wave-lengths and the 
