At the Parkes Museum of Hygiene, London, Dr. Robert J. Lee recently
delivered a lecture on the above subject, illustrated by experiments.
The author remarked that he could not better open up his theme than
by explaining what was meant by disinfection. He would do so by an
illustration from Greek literature. When Achilles had slain Hector,
the body still lay on the plain of Troy for twelve days after; the
god Hermes found it there and went and told of it--"This, the twelfth
evening since he rested, untouched by worms, untainted by the air."
The Greek word for taint in this sense was _sepsis_, which meant
putrefaction, and from this we had the term "antiseptic," or that which
was opposed to or prevented putrefaction. The lecturer continued:
I have here in a test tube some water in which a small piece of meat was
placed a few days ago. The test tube has been in rather a warm room, and
the meat has begun to decompose. What has here taken place is the first
step in this inquiry. This has been the question at which scientific
men have been working, and from the study of which has come a valuable
addition to surgical knowledge associated with the name of Professor
Lister, and known as antiseptic. What happens to this meat, and what is
going on in the water which surrounds it? How long will it be before all
the smell of putrefaction has gone and the water is clear again? For
it does in time become clear, and instead of the meat we find a fine
powdery substance at the bottom of the test tube. It may take weeks
before this process is completed, depending on the rate at which it
goes on. Now, if we take a drop of this water and examine it with the
microscope, we find that it contains vast numbers of very small living
creatures or "organisms." They belong to the lowest forms of life, and
are of very simple shape, either very delicate narrow threads or rods or
globular bodies. The former are called bacteria, or staff-like bodies;
the latter, micrococci. They live upon the meat, and only disappear when
the meat is consumed. Then, as they die and fall to the bottom of the
test tube, the water clears again.
Supposing now, when the meat is first put into water, the water is made
to boil, and while boiling a piece of cotton wool is put into the
mouth of the tube. The tube may be kept in the same room, at the same
temperature as the unboiled one, but no signs of decomposition will be
found, however long we keep it. The cotton wool prevents it; for we may
boil the water with the meat in it, but it would not be long before
bacteria and micrococci are present if the wool is not put in the mouth
of the test tube. The conclusion you would naturally draw from this
simple but very important experiment is that the wool must have some
effect upon the air, for we know well that if we keep the air out we
can preserve meat from decomposing. That is the principle upon which
preserved meats and fruits are prepared. We should at once conclude that
the bacteria and micrococci must exist in the air, perhaps not in the
state in which we find them in the water, but that their germs or eggs
are floating in the atmosphere. How full the air may be of these germs
was first shown by Professor Tyndall, when he sent a ray of electric
light through a dark chamber, and as if by a magician's wand revealed
the multitudinous atomic beings which people the air. It is a beautiful
thing to contemplate how one branch of scientific knowledge may assist
another; and we would hardly have imagined that the beam of the electric
light could thus have been brought in to illumine the path of the
surgeon, for it is on the exclusion of these bacteria that it is found
the success of some great operation may depend. It is thus easy to
understand how great an importance is to be attached to the purity of
air in which we live. This is the practical use of the researches to
which the art of surgery is so much indebted; and not surgery alone,
but all mankind in greater or less degree. Professor Tyndall has gone
further than this, and has shown us that on the tops of lofty mountains
the air is so pure, so free from organisms, that decomposition is
impossible.
Now, supposing we make another experiment with the test tube, and
instead of boiling we add to its contents a few drops of carbolic acid;
we find that decomposition is prevented almost as effectually as by the
use of the cotton wool. There are many other substances which act like
carbolic acid, and they are known by the common name of antiseptics or
antiseptic agents. They all act in the same way; and in such cases as
the dressing of wounds it is more easy to use this method of excluding
bacteria than by the exclusion of the air or by the use of cotton wool.
We have here another object for inquiry--viz., the particular property
of these different antiseptics, the property which they possess of
preventing decomposition. This knowledge is _very_ ancient indeed. We
have the best evidence in the skill of the Egyptians in embalming the
dead. These substances are obtained from wood or coal, which once was
wood. Those woods which do not contain some antiseptic substance, such
as a gum or a resin, will rot and decay. I am not sure that we can
give a satisfactory reason for this, but it is certain that all these
substances act as antiseptics by destroying the living organisms which
are the cause of putrefaction. Some are fragrant oils, as, for example,
clove, santal, and thyme; others are fragrant gums, such as gum bezoin
and myrrh. A large class are the various kinds of turpentine obtained
from pine trees. We obtain carbolic acid from the coal tar largely
produced in the manufacture of gas. Both wood tar, well known under the
name of creosote, and coal tar are powerful antiseptics. It is easy to
understand by what means meat and fish are preserved from decomposition
when they have been kept in the smoke of a wood fire. The smoke contains
creosote in the form of vapor, and the same effect is produced on the
meat or fish by the smoke as if they had been dipped in a solution of
tar--with this difference, that they are dried by the smoke, whereas
moisture favors decomposition very greatly.
I can show why a fire from which there is much smoke is better than one
which burns with a clear flame, by a simple experiment. Here is a piece
of gum benzoin, the substance from which Friar's balsam is made. This
will burn, if we light it, just as tar burns, and without much smoke or
smell. If, instead of burning it, we put some on a spoon and heat it
gently, much more smoke is produced, and a fragrant scent is given off.
In the same way we can burn spirit of lavender or eau de Cologne, but we
get no scent from them in this way, for the burning destroys the scent.
This is a very important fact in the disinfection of the air. The less
the flame and the larger the quantity of smoke, the greater the effect
produced, so far as disinfection is concerned. As air is a vapor, we
must use our disinfectants in the form of vapor, so that the one may mix
with the other, just as when we are dealing with fluids we must use a
fluid disinfectant.
The question that presents itself is this: Can we so diffuse the vapor
of an antiseptic like carbolic acid through the air as to destroy the
germs which are floating in it, and thus purify it, making it like air
which has been filtered through wool, or like that on the top of a lofty
mountain? If the smoke of a wood fire seems to act as an antiseptic,
and putrefaction is prevented, it seems reasonable to conclude that air
could be purified and made antiseptic by some proper and convenient
arrangement. Let us endeavor to test this by a few experiments.
Here is a large tube 6 inches across and 2 feet long, fixed just above a
small tin vessel in which we can boil water and keep it boiling as long
as we please. If we fill the vessel with carbolic acid and water and
boil it very gently, the steam which rises will ascend and fill the tube
with a vapor which is strong or weak in carbolic acid, according as we
put more or less acid in the water. That is to say, we have practically
a chimney containing an antiseptic vapor, very much the same thing as
the smoke of a wood fire. We must be able to keep the water boiling, for
the experiment may have to be continued during several days, and during
this time must be neither stronger nor weaker in carbolic acid, neither
warmer nor colder than a certain temperature. This chimney must be
always at the same heat, and the fire must therefore be kept constantly
burning. This is easily accomplished by means of a jet of gas, and
by refilling the vessel every 24 hours with the same proportions of
carbolic acid and water.
The question arises, how strong must this vapor be in carbolic acid to
act as an antiseptic? It is found that 1 part acid to 50 of water is
quite sufficient to prevent putrefaction. If we keep this just below
boiling point there will be a gentle and constant rising of steam into
the cylinder, and we can examine this vapor to see if it is antiseptic.
We will take two test tubes half filled with water and put a small piece
of beef into each of them and boil each for half a minute. One test
tube we will hang up inside the cylinder, so that it is surrounded by
carbolic acid vapor. The other we stand up in the air. If the latter is
hung in a warm room, decomposition will soon take place in it; will the
same thing happen to the other cylinder? For convenience sake we had
best put six tubes inside the cylinder, so that we can take one out
every day for a week and examine the contents on the field of a
microscope. It will be necessary to be very particular as to the
temperature to which the tubes are exposed, and the rates of evaporation
beneath the cylinder. I may mention that on some of the hottest days of
last summer I made some experiments, when the temperature both of
the laboratory and inside the cylinder was 75°F. I used test tubes
containing boiled potatoes instead of meat, and found that the tube in
the air, after 48 hours, abounded not simply with bacteria and other
small bodies present in decomposition, but with the large and varied
forms of protozoa, while the tube inside the cylinder contained no signs
of decomposition whatever. When the room was cold the experiments were
not so satisfactory, because in the former case there was very little if
any current of air in the cylinder. This leads us to the question, why
should we not make the solution of carbolic acid and water, and heat it,
letting the steam escape by a small hole, so as to produce a jet? It is
a singular fact that for all practical purposes such a steam jet will
contain the same proportion of acid to water as did the original
solution. The solution can of course be made stronger or weaker till we
ascertain the exact proportion which will prevent decomposition.
From this arises naturally the question, what quantity of vapor must be
produced in a room in order to kill the bacteria in its atmosphere? If
we know the size of the room, shall we be able tell? These questions
have not yet been answered, but the experiments which will settle them
will be soon made, I have no doubt, and I have indicated the lines upon
which they will be made. I have here a boiler of copper into which we
can put a mixture, and can get from it a small jet of steam for some
hours. A simple experiment will show that no bacteria will exist in that
vapor. If I take a test tube containing meat, and boil it while holding
the mouth of it in this vapor, after it has cooled we close the mouth
with cotton wool, and set it aside in a warm place; after some days we
shall find no trace of decomposition, but if the experiment is repeated
with water, decomposition will soon show itself. Of course, any strength
of carbolic acid can be used at will, and will afford a series of tests.
There are other methods of disinfecting the atmosphere which we cannot
consider this evening, such as the very potent one of burning sulphur.
In conclusion, the lecturer remarked that his lecture had been cast into
a suggestive form, so as to set his audience thinking over the causes
which make the air impure, and how these impurities are to be prevented
from becoming deleterious to health.
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