]
ANÆSTHETICS.
The discovery which is indicated by the somewhat unfamiliar word[16]
which heads this article is perhaps the greatest which has ever been
made in connection with the science of medicine. At least, there is no
other discovery of modern times which has so largely and directly
contributed to the assuagement of human suffering. Nay, in this respect
there is perhaps in the whole annals of the healing art no other which
can rival it, if we except that famous one of Jenner’s which has
arrested the ravages of small-pox. During the last thirty years, all the
more formidable operations of the surgeon have been, in almost every
case, performed with a happy unconsciousness on the part of the patient.
In unconsciousness, induced by the same means, has relief also been
found for severe suffering arising from other causes. The substances
which are denoted by the word “anæsthetics” differ from the drugs which
the older surgeons sometimes administered before an operation, in order
to lull the patient’s sense of pain. They differ in their nature and in
the mode of their administration; by the certainty and completeness of
their action; by the entirely transient effects they produce, which pass
off without leaving a trace.
Footnote 16:
From α (αν), privative, and αισθητικος, capable of perceiving or
feeling.
To the great chemist whose name has already been mentioned as the
discoverer of the metals of the alkalies and alkaline earths we are
indebted for the first of the remarkable class of bodies we are about to
discuss. The first work that Davy published had for its title
“Researches, Chemical and Philosophical, chiefly concerning Nitrous
Oxide and its Respiration.” This was in the year 1800, when the
philosopher had hardly completed his twenty-first year. The work caused
no little sensation in the scientific world, and it was in consequence
of the reputation he acquired by these researches that Davy was
appointed to the chemical professorship at the Royal Institution. Davy
was not the original discoverer of nitrous oxide, but he first entered
upon a full investigation of its properties, and announced the singular
effect produced by its inhalation. The kind of transient intoxication
and propensity to laughter which it excites have obtained for this
compound the familiar name of _laughing gas_. Davy had by experiment on
his own person proved the anæsthetic properties of this gas, for he had
a tooth painlessly extracted when under its influence, and he says in
the work above named that “as nitrous acid gas seems capable of
destroying pain, it could probably be used with advantage in surgical
operations where there is no effusion of blood.” Davy’s observations and
suggestions were destined to lie barren for nearly half a century, but
they nevertheless formed the basis of the great results which have since
been attained.
Before proceeding farther, it will perhaps be well to make the
unscientific reader acquainted with the chemistry of nitrous oxide. We
may presume that he knows that atmospheric air is a _mixture_ of the two
invisible gases, nitrogen and oxygen (the small quantity of carbonic
acid also present need not now be considered). When a known quantity of
air is passed over red-hot copper turnings, contained in a tube, the
whole of the oxygen is seized upon by the copper, and only the nitrogen
issues from the tube, and may be collected. Some of the copper is thus
converted into oxide, and the increase of the weight of the tube’s
contents shows the weight of oxygen contained in the air, while the
weight of nitrogen may be known from the volume collected. In this way
the chemist analyses atmospheric air, and determines that 100 parts by
weight of dry air contain about 79 of nitrogen and 21 of oxygen; or, by
measure, about four times as much of the former as of the latter. Now,
chemists are acquainted with no fewer than five _different_ substances
which contain nothing but nitrogen and oxygen. These substances are
either gases, or can be changed into the gaseous form by heat, and they
can all be analysed in the same manner as air. The results of such
analyses show in 100 parts by weight of each substance the following
proportions of its constituents:
┌────────┬──────┬──────┬──────┬──────┬──────┐
│ │No. 1.│No. 2.│No. 3.│No. 4.│No. 5.│
├────────┼──────┼──────┼──────┼──────┼──────┤
│Nitrogen│63·64 │46·67 │36·84 │30·44 │25·93 │
│Oxygen │36·36 │53·33 │63·16 │69·56 │74·07 │
└────────┴──────┴──────┴──────┴──────┴──────┘
In casting the eye over this table, no relation will probably be
detected between the five cases. But if we write down, not the
quantities of nitrogen and oxygen contained in 100 parts of each
compound, but the quantity of oxygen which in each compound is united to
some fixed quantity of nitrogen, we shall at once detect a remarkable
law: thus, taking 28 as the fixed weight of nitrogen, for reasons which
need not be here explained:
┌────────┬──────┬──────┬──────┬──────┬──────┐
│ │No. 1.│No. 2.│No. 3.│No. 4.│No. 5.│
├────────┼──────┼──────┼──────┼──────┼──────┤
│Nitrogen│ 28 │ 28 │ 28 │ 28 │ 28 │
│{Oxygen │ 16 │ 32 │ 48 │ 64 │ 80 │
│{ or │16 × 1│16 × 2│16 × 3│16 × 4│16 × 5│
└────────┴──────┴──────┴──────┴──────┴──────┘
Chemists have a sort of shorthand method of expressing the composition
of substances, which may be conveniently illustrated by the case before
us. Let it be agreed that the letter N shall not only represent
nitrogen, but always _fourteen_ parts by weight—grains, ounces, &c.,
&c.,—of nitrogen; and that, similarly, O shall stand for _sixteen_ parts
by weight of oxygen. It is plain that the composition of the compound
No. 2 may be represented by simply writing down “NO;” and that of No. 4,
in which there is just double the proportion of oxygen, by “NOO.” But to
avoid an unnecessary repetition of the same symbol, when it has to be
taken more than once, a small figure is written after and a little below
it. Thus, for OO, “O_{2}” is written. The proportional composition of
each of the five compounds will now be obvious from the following
symbols:
┌────────────┬────────────┬────────────┬────────────┬────────────┐
│ No. 1. │ No. 2. │ No. 3. │ No. 4. │ No. 5. │
├────────────┼────────────┼────────────┼────────────┼────────────┤
│ N_{2}O │ NO │ N_{2}O_{3} │ NO_{2} │ N_{2}O_{5} │
└────────────┴────────────┴────────────┴────────────┴────────────┘
These symbols may be regarded as merely a compendious expression of the
composition of each substance—as a shorthand statement of the _facts_ of
analysis. But to the majority of chemists the symbols have a deeper
significance; for they are taken as representing the _atoms_ of each
element which enter into each smallest possible particle of a compound;
they express a certain theory of the ultimate constitution of matter.
Thus, if we suppose that there exist indivisible particles of nitrogen
and of oxygen, and that each smallest particle, or _molecule_, of the
compounds under consideration is constituted of a certain definite and
invariable number of each kind of atoms; and, further, if we suppose
that an _atom_ of oxygen is heavier than one of nitrogen in the
proportion of 16 to 14, or 8 to 7, we shall have a simple theoretical
_explanation_ of the relations in the proportions already pointed out.
In fact, these would result from the simplest combinations of the two
kinds of _atoms_; and we can picture each one of the smallest particles
of the several bodies as thus constituted:
┌────────────┬────────────┬────────────┬────────────┬────────────┐
│ No. 1. │ No. 2. │ No. 3. │ No. 4. │ No. 5. │
├────────────┼────────────┼────────────┼────────────┼────────────┤
│ ● ● │ │ ● ● │ ● │ ● ● │
│ ○ │ ● ○ │ ○ ○ ○ │ ○ ○ │ ○ ○ ○ │
│ │ │ │ │ ○ ○ │
├────────────┼────────────┼────────────┼────────────┼────────────┤
│ N_{2}O │ NO │ N_{2}O_{3} │ NO_{2} │ N_{2}O_{5} │
└────────────┴────────────┴────────────┴────────────┴────────────┘
The black circles represent nitrogen atoms, and the open ones oxygen
atoms; the symbols are placed below in order that their relation to the
supposed atomic constitution may be obvious at a glance. While the
symbol of a compound must always accord with its percentage composition,
the latter does of itself determine the symbol or formula. A number of
other circumstances, which cannot here be discussed, are taken into
account as evidence of the constitution of the molecule.
This digression on chemical formulæ will, it is hoped, enable the
general reader, who may not previously have been acquainted with them,
to perceive their significance, instead of passing them over as
unintelligible cabalistic letters when they occur in the following
pages. With this object, it may be added that the elements, hydrogen,
carbon, and chlorine, are respectively represented by H, C, and Cl; and
that the proportional quantities, which are also implied in the symbols,
and are those by which H, C, and Cl combine with other bodies, are 1,
12, and 35·5 respectively. Another point which should be understood is
that the properties and behaviour of a chemical compound are different,
and usually extremely different, from those of any of its constituents.
This is well illustrated in the subject we are considering. Atmospheric
air is a _mixture_ (not a compound) of nitrogen and oxygen gases, and
all its properties are intermediate between those of its ingredients
taken separately. Nitrous oxide, N_{2}O, has properties not possessed by
either constituent separately. For example, it is very soluble in water,
whereas oxygen is very slightly so, and nitrogen still less. The other
compounds we have referred to differ widely from nitrous oxide and from
each other in their properties.
Nitrous oxide is an invisible gas, having a slightly sweetish taste and
smell. It is dissolved by water, which, at ordinary temperatures, takes
up about three-fourths of its volume of the gas. By cold and great
pressure the gas may be condensed into a colourless liquid. The gas is
obtained in a pure state by gently heating the salt called ammonium
nitrate, which is formed by neutralizing pure nitric acid with carbonate
of ammonia. The action which occurs may be explained thus: the hydrogen
of the ammonium unites with a portion of the oxygen of the nitric acid,
forming water, whilst the remainder of the oxygen combines with the
nitrogen. As chemical actions are regarded as either separations or
unions of atoms, they can be expressed by what is called a _chemical
equation_, the left-hand side of which shows the arrangement of the
atoms before the action, and the right-hand side the arrangement after
it, the sign of equality being read as “produce” or “produces.” But the
validity of the equations, like that of the symbolic formulæ, is quite
independent of the existence of atoms; for the equation always rests on
certain facts, namely, the relations between the quantities of the
substances which enter into, and those which are produced by, a chemical
action. Thus, in the present case the action may be symbolically
expressed as follows:
H_{4}N NO_{3} = 2H_{2}O + N_{2}O
Ammonium nitrate. Water. Nitrous oxide.
The equation expresses the fact that every 80 parts by weight of
ammonium nitrate, which are used in this reaction, split up into 36 of
water and 44 of nitrous oxide.
No attempt seems to have been made to turn Davy’s suggestion to
practical account; but in courses of chemical lectures at the hospitals
and elsewhere the peculiar physiological properties of nitrous oxide
have, since Davy’s announcement, always been demonstrated by some person
inhaling the gas. In the medical schools the students often operated on
a comrade who was under the influence of nitrous oxide to the extent of
bestowing sundry pinches and cuffs, which fully proved the anæsthetic
qualities of the nitrous oxide. In 1818 Faraday pointed out the
similarity between the effects of _ether_ and of nitrous oxide, and from
that time Professor Turner regularly included among the experiments of
his course of chemistry the inhalation of the vapour of ether by one of
the students. This was done by simply pouring a little ether into a
bladder of air, and by means of a tube drawing the mixed air and vapour
into the mouth. Until 1844 the effects of nitrous oxide and of ether
vapour remained without application, although thus continually
demonstrated in lectures. At the close of that year, Mr. Horace Wells, a
dentist, of Hartford, Connecticut, U.S.A., witnessed the usual
experiments with nitrous oxide at a public lecture. At his request the
lecturer attended at Mr. Wells’s residence the following day, to
administer to him the nitrous oxide, in order that he might try its
efficacy in annulling pain, for he was himself to have a tooth extracted
by a brother dentist. His exclamation on finding the operation
painlessly over was, “A new era in tooth-pulling!” Mr. Wells continued
his experiments on the use of nitrous oxide in dental operations, but he
did not apparently obtain uniform results, for he pronounced its effects
uncertain, and he gave it up. On the occasion when Mr. Wells’s tooth was
extracted, Dr. W. T. G. Morton was present, and he soon afterwards found
that under the influence of ether vapour, teeth might be painlessly
extracted and surgical operations performed. Dr. Morton attempted to
conceal the substance he used under the name of “letheon,” for which he
obtained a patent. But the well-known and characteristic odour of ether
declared the nature of the “letheon;” and Dr. Bigelow having in
consequence tried ether, found it to produce all the effects of
“letheon.” So the matter was no longer a secret. Dr. Morton was,
therefore, the person who first applied ether vapour, and the extraction
of a tooth was the occasion of its first application. This was in 1846.
It was used for the first time in England on the 19th of December, 1846,
also for the extraction of a tooth; and two days afterwards Mr. Liston,
the eminent surgeon, performed the operation of amputating the thigh
while his patient was under the influence of ether. The employment of
ether in surgical operations quickly spread, and its administration in
hospitals became general throughout Europe and America.
The chemical constitution of ether, and its relation to alcohol, may be
indicated by the following formulæ:
HOH HO(C_{2}H_{5}) (C_{2}H_{5})O(C_{2}H_{5})
Water. Alcohol. Ether.
If we suppose one of the hydrogen atoms in the molecule of water to be
removed and replaced by the group (C_{2}H_{5}), the result is alcohol.
If, now, (C_{2}H_{5}) be substituted in the alcohol for the remaining
atom of hydrogen, we get a particle of _ether_. Ether was discovered in
1540, and described as sweet oil of vitriol, but its real nature was
first pointed out by Liebig. It is prepared by distilling a mixture of
sulphuric acid and alcohol. It is a colourless transparent liquid,
extremely volatile, and possessing a peculiar and powerful odour. It
evaporates so rapidly that a drop allowed to fall from a bottle on a
warm day may be converted into vapour before it reaches the ground. When
its vapour is inhaled in sufficient proportion mixed with air, it soon
produces a complete insensibility to pain. In the case of a full-grown
man who inhales air containing 45 per cent. of the vapour, about 2 drams
per minute of the liquid are consumed. The air is allowed to stream over
the surface of the liquid in a proper apparatus, where it takes up the
vapour, and the two pass through a flexible tube to a piece fitting over
the mouth and nostrils of the patient. The effects produced are
progressive, and may be thus described:
For about two minutes after the beginning of the inhalation, the patient
retains his mental faculties, and has some power of controlling his
movements, but in a confused and disordered manner. At the end of the
third minute he is unconscious; there are no voluntary movements, but
muscular contractions may agitate the frame. At the end of the fourth
minute, the only perceptible movements are the motions of the chest in
respiration. If the inhalation be discontinued at the end of the fourth
minute, when 1 oz. of ether will have evaporated, similar stages are
passed through in reverse order during recovery. The condition reached
at the end of the fourth minute continues about two minutes; the
intermediate state lasts three or four minutes; the condition of
confused intellect and will about five minutes. This is succeeded by a
feeling of intoxication and exhilaration, which continues for ten or
fifteen minutes. It was probably this excitement of the system produced
by ether which has caused it to be superseded—in Britain, at least—in
about twelve months after its adoption, by _chloroform_.
Chloroform appears to have been independently discovered in 1831, by
Soubeiran, and by an American chemist, Guthrie. It is usually procured
by distilling a mixture of bleaching powder, spirits of wine, and water.
Chloroform is a colourless volatile liquid, of an odour much more
agreeable than that of ether. Its composition is represented by
CHCl_{3}. The merit of having first applied the singular properties of
this substance to the alleviation of human suffering belongs to the late
Sir J. Y. Simpson, of Edinburgh. Its use as an anæsthetic was apparently
suggested to this eminent professor by Mr. Waldie, of Liverpool. It was
first applied at Edinburgh on the 15th November, 1847; and when its
efficacy had been proved, it was soon extensively used, and in Europe,
at least, almost entirely superseded ether, as being more rapid and
certain in its action, not producing injurious excitement, and being
pleasanter to inhale. A notion prevailed that chloroform was not only
more powerful in its operation than ether, but also more safe. In
January, 1848, its administration, however, proved fatal to a patient;
and since then a certain number of casualties of this kind have occurred
with chloroform, ether, and other anæsthetics.
The patient is often made to inhale the vapour of chloroform by merely
holding before his mouth and nostrils a sponge or handkerchief, on which
a small quantity of the liquid has been poured. Dr. Snow contrived an
apparatus for administering the vapour with more regularity. A metal box
adapted to the shape of the face is made to cover the mouth and
nostrils. This piece has two valves, one of which admits the air and
vapour from an elastic tube connected with the apparatus containing the
chloroform, and prevents its return; the other valve is a flap opening
outwards, which allows the expired air to escape. There is also an
adjustment for admitting directly into the mouthpiece more or less
atmospheric air.
The sensations first experienced when chloroform is inhaled are said to
be agreeable. Many persons have described the feeling as resembling
rapid travelling in a railway carriage; there is a singing in the ears,
and when the power of vision ceases, and the person is no longer
conscious of light, the sensation is that of entering a tunnel. After
this there is a lessened sensibility to pain; and in the next stage the
unconsciousness to outward impressions is deeper, but the mental
faculties, though impaired, are not wholly suspended, for the patient
may speak, and usually dreams something which he afterwards remembers.
When the person is still more under the influence of the chloroform, no
voluntary motions take place, although there may be some inarticulate
muttering. Dr. Snow describes several conditions which may be observed
in patients undergoing operations under the influence of chloroform.
First, the patient may preserve the most perfect quietude without a sign
of consciousness or sensation; this is the most usual condition. Second,
he may moan, or cry, or flinch under the operation, without, however,
having the least memory of any pain when he recovers. Third, the patient
may talk, laugh, or sing during the operation; but what he says is
altogether devoid of reference to what is done. Fourth, he may be
conscious of what is taking place, and may look on while some minor
operation is proceeding, without feeling it, or without feeling it
painfully. This is often the condition of the patient as the effect is
passing off, while some smaller operation is still proceeding. Fifth,
the patient may complain he is being hurt; but afterwards, when the
effect of the chloroform has passed off, he will assert that he felt no
pain whatever. When the chloroform has been inhaled for but a short
time, the patient becomes conscious in about five minutes after its
discontinuance; but with a longer inhalation the period of
unconsciousness may last for perhaps ten minutes. The return of
consciousness takes place with tranquillity: not unfrequently the
patient’s first speech, even after a serious operation, often being an
assertion that the chloroform has not taken effect.
In the strongest degree of ether and chloroform effects, all the muscles
of the body are relaxed; the limbs hang down, or rest in any position in
which they are placed; the eyelids droop over the eyes, or remain as
they are placed by the finger; the breathing is deep, regular, and
automatic; there is often snoring, and this is, indeed, characteristic
of the deepest degree of unconsciousness; the relaxation of the muscles
renders the face devoid of expression, and with a placid appearance, as
if the person were in a sound natural sleep. He is perfectly passive
under every kind of operation. The breathing and the action of the heart
proceed all the while with unimpaired regularity. It is, however, known
by experiments on animals that if the inhalation be prolonged beyond the
period necessary to produce these effects, the respiratory functions are
interfered with by the insensibility extending to the nerves on which
they depend. The breathing of an animal thus treated becomes irregular,
feeble, or laborious, and death ensues. However nearly dead from
inhalation of ether vapour the animal may be, provided respiration has
not actually ceased, it always recovers when allowed to breathe fresh
air. Of course, the etherization is never carried to this stage with
human beings.
Air containing 2 grs. of chloroform in 100 cubic inches suffices to
induce insensibility; but 5 grs. in 100 cubic inches is found a more
suitable proportion. Dr. Snow, who strongly disapproved of the uncertain
and irregular mode of administering chloroform on a handkerchief or
sponge, contrived the inhaling apparatus already described. The air
before reaching the mouth and nostrils of the patient passes through a
vessel containing bibulous paper moistened with chloroform. This vessel
he surrounds with water at the ordinary temperature of the air, in order
to supply the heat absorbed by the conversion of the liquid into vapour,
so that the formation of the latter may go on regularly. The same
thoughtful arrangement formed part of the ether-inhaler he had
previously contrived.