and significance of which are at once revealed by the luminous beam.
He prepared twenty one flasks, each containing a decoction of yeast,
filtered and clear. He boiled the decoction so as to destroy whatever
germs it might contain, and, while the space above the liquid was
filled with pure steam, he sealed his flasks with a blow-pipe. He
opened ten of them in the deep, damp caves of the Paris Observatory,
and eleven of them in the courtyard of the establishment. Of the
former, one only showed signs of life subsequently. In nine out of
the ten flasks no organisms of any kind were developed. In all the
others organisms speedily appeared.
Now here is an experiment conducted in Paris, on which we can throw
obvious light in London. Causing our luminous beam to pass through a
large flask filled with the air of this room, and charged with its
germs and its dust, the beam is seen crossing the flask from side to
side. But here is another similar flask, which cuts a clear gap out
of the beam. It is filled with _unfiltered_ air, and still no trace of
the beam is visible. Why? By pure accident I stumbled on this flask
in our apparatus room, where it had remained quiet for some time.
Acting upon this obvious suggestion I set aside three other flasks,
filled, in the first instance, with mote-laden air. They are now
optically empty. Our former experiments proved that the
life-producing particles attach themselves to the fibres of
cotton-wool. In the present experiment the motes have been brought by
gentle air-currents, established by slight differences of temperature
within our closed vessels, into contact with the interior surface, to
which they adhere. The air of these flasks has deposited its dust,
germs and all, and is practically free from suspended matter.
I had a chamber erected, the lower half of which is of wood, its upper
half being enclosed by four glazed window-frames. It tapers to a
truncated cone at the top. It measures in plan 3 ft. by 2 ft. 6 in,
and its height is 5 ft. 10 in. On February 6 it was closed, every
crevice that could admit dust, or cause displacement of the air, being
carefully pasted over with paper. The electric beam at first revealed
the dust within the chamber as it did in the air of the laboratory.
The chamber was examined almost daily; a perceptible diminution of the
floating matter being noticed as time advanced. At the end of a week
the chamber was optically empty, exhibiting no trace of matter
competent to scatter the light. Such must have been the case in the
stagnant caves of the Paris Observatory. Were our electric beam sent
through the air of these caves its track would be invisible; thus
showing the indissoluble association of the scattering of light by air
and its power to generate life.
I will now turn to what seems to me a more interesting application of
the luminous beam than any hitherto described. My reference to
Professor Lister's interpretation of the fact, that air which has
passed through the lungs cannot produce putrefaction, is fresh in your
memories. 'Why air,' said he, 'introduced into the pleural cavity,
through a wounded lung, should have such wholly different effects from
that entering through a permanently open wound, penetrating from
without, was to me a complete mystery, till I heard of the germ
theory of putrefaction, when it at once occurred to me that it was
only natural that the air should be filtered of germs by the air
passages, one of whose offices is to arrest inhaled particles of
dust, and prevent them from entering the air-cells.'
Here is a surmise which bears the stamp of genius, but which needs
verification. If, for the words 'it is only natural' we were
authorised to write 'it is perfectly certain,' the demonstration would
be complete. Such demonstration is furnished by experiments with a
beam of light. One evening, towards the close of 1869, while pouring
various pure gases across the dusty track of a luminous beam, the
thought occurred to me of using my breath instead of the gases. I
then noticed, for the first time, the extraordinary darkness produced
by the expired air, _towards the end of the expiration_. Permit me to
repeat the experiment in your presence. I fill my lungs with ordinary
air and breathe through a glass tube across the beam. The
condensation of the aqueous vapour of the breath is shown by the
formation of a luminous white cloud of delicate texture. We abolish
this cloud by drying the breath previous to its entering the beam; or,
still more simply, by warming the glass tube. The luminous track of
the beam is for a time uninterrupted by the breath, because the dust
returning from the lungs makes good, in great part, the particles
displaced. After a time, however, an obscure disk appears in the
beam, the darkness of which increases, until finally, towards the end
of the expiration, the beam is, as it were, pierced by an intensely
black hole, in which no particles whatever can be discerned. The
deeper air of the lungs is thus proved to be absolutely free from
suspended matter. It is therefore in the precise condition required
by Professor Lister's explanation. This experiment may be repeated
any number of times with the same result. I think it must be regarded
as a crowning piece of evidence both of the correctness of Professor
Lister's views and of the impotence, as regards vital development, of
optically pure air. [Footnote: Dr. Burden Sanderson draws attention to
the important observation of Brauell, which shows that the _contagium_
of a pregnant animal, suffering from splenic fever, is not found in
the blood of the foetus; the placental apparatus acting as a filter,
and holding back the infective particles.]
Application of Luminous beams to Water.
The method of examination here pursued is also applicable to water. It
is in some sense complementary to that of the microscope, and may, I
think, materially aid enquiries conducted with that instrument. In
microscopic examination attention is directed to a small portion of
the liquid, and the aim is to detect the individual particles. By the
present method a large portion of the liquid is illuminated, the
collective action of the particles being revealed, by the scattered
light. Care is taken to defend the eye from the access of all other
light, and, thus defended, it becomes an organ of inconceivable
delicacy. Indeed, an amount of impurity so infinitesimal as to be
scarcely expressible in numbers, and the individual particles of which
are so small as wholly to elude the microscope, may, when examined by
the method alluded to, produce not only sensible, but striking,
effects upon the eye.
We will apply the method, in the first place, to an experiment of M.
Pouchet intended to prove conclusively that animalcular life is
developed in cases where no antecedent germs could possibly exist. He
produced water from the combustion of hydrogen in air, justly arguing
that no germ could survive the heat of a hydrogen flame. But he
overlooked the fact that his aqueous vapour was condensed in the air,
and was allowed as water to trickle through the air. Indeed the
experiment is one of a number by which workers like M. Pouchet are
differentiated from workers like Pasteur. I will show you some water,
produced by allowing a hydrogen flame to play upon a polished silver
condenser, formed by the bottom of a silver basin, containing ice. The
collected liquid is pellucid in the common light; but in the condensed
electric beam it is seen to be laden with particles, so thick-strewn
and minute as to produce a continuous luminous cone. In passing
through the air the water loaded itself with this matter; and the
deportment of such water could obviously have no influence in deciding
this great question.
We are invaded with dirt not only in the air we breathe, but in the
water we drink. To prove this I take the bottle of water intended to
quench your lecturer's thirst; which, in the track of the beam, simply
reveals itself as dirty water. And this water is no worse than the
other London waters. Thanks to the kindness of Professor Frankland, I
have been furnished with specimens of the water of eight London
companies. They are all laden with impurities mechanically suspended.
But you will ask whether filtering will not remove the suspended
matter? The grosser matter, undoubtedly, but not the more finely
divided matter. Water may be passed any number of times through
bibulous paper, it will continue laden with fine matter. Water passed
through Lipscomb's charcoal filter, or through the filters of the
Silicated Carbon Company, has its grosser matter removed, but it is
thick with fine matter. Nine-tenths of the light scattered by these
suspended particles is perfectly polarised in a direction at right
angles to the beam, and this release of the particles from the
ordinary law of polarisation is a demonstration of their smallness. I
should say by far the greater number of the particles concerned in
this scattering are wholly beyond the range of the microscope, and no
ordinary filter can intercept such particles. It is next to
impossible, by artificial means, to produce a pure water. Mr.
Hartley, for example, some time ago distilled water while surrounded
by hydrogen, but the water was not free from floating matter. It is
so hard to be clean in the midst of dirt. In water from the Lake of
Geneva, which has remained long without being stirred, we have an
approach to the pure liquid. I have a bottle of it here, which was
carefully filled for me by my distinguished friend Soret. The track
of the beam through it is of a delicate sky-blue; there is scarcely a
trace of grosser matter.
The purest water that I have seen--probably the purest which has been
seen hitherto--has been obtained from the fusion of selected specimens
of ice. But extraordinary precautions are required to obtain this
degree of purity. The following apparatus has been constructed for
this purpose: Through the plate of an air-pump passes the shank of a
large funnel, attached to which below the plate is a clean glass bulb.
In the funnel is placed a block of the most transparent ice, and over
the funnel a glass receiver. This is first exhausted and refilled
several times with air, filtered by its passage through cotton-wool,
the ice being thus surrounded by pure moteless air. But the ice has
previously been in contact with mote-filled air; it is therefore
necessary to let it wash its own surface, and also to wash the bulb
which is to receive the water of liquefaction. The ice is permitted
to melt, the bulb is filled and emptied several times, until finally
the large block dwindles to a small one. We may be sure that all
impurity has been thus removed from the surface of the ice. The water
obtained in this way is the purest hitherto obtained. Still I should
hesitate to call it absolutely pure. When condensed light is sent
through it, the track of the beam is not invisible, but of the most
exquisitely delicate blue. This blue is purer than that of the sky,
so that the matter which produces it must be finer than that of the
sky. It may be and indeed has been, contended that this blue is
scattered by the very molecules of the water, and not by matter
suspended in the water. But when we remember that this perfection of
blue is approached gradually through stages of less perfect blue; and
when we consider that a blue in all respects similar is demonstrably
obtainable from particles mechanically suspended, we should hesitate,
I think, to conclude that we have arrived here at the last stage of
purification. The evidence, I think, points distinctly to the
conclusion that, could we push the process of purification still
farther, even this last delicate trace of blue would disappear.
Chalk-water. Clark's Softening Process.
But is it not possible to match the water of the Lake of Geneva here
in England? Undoubtedly it is. We have in England a kind of rock
which constitutes at once an exceedingly clean recipient and a natural
filter, and from which we can obtain water extremely free from
mechanical impurities. I refer to the chalk formation, in which large
quantities of water are held in store. Our chalk hills are in most
cases covered with thin layers of soil, and with very scanty
vegetation. Neither opposes much obstacle to the entry of the rain
into the chalk, where any organic impurity which the water may carry
in is soon oxidised and rendered harmless. Those who have scampered
like myself over the downs of Hants and Wilts will remember the
scarcity of water in these regions. In fact, the rainfall, instead of
washing the surface and collecting in streams, sinks into the fissured
chalk and percolates through it. When this formation is suitably
tapped, we obtain water of exceeding briskness and purity. A large
glass globe, filled with the water of a well near Tring, shows itself
to be wonderfully free from mechanical impurity. Indeed, it stands to
reason that water wholly withdrawn from surface contamination, and
percolating through so clean a substance, should be pure. It has been
a subject much debated, whether the supply of excellent water which
the chalk holds in store could not be rendered available for London.
Many of the most eminent engineers and chemists have ardently
recommended this source, and have sought to show, not only that its
purity is unrivalled, but that its quantity is practically
inexhaustible. Data sufficient to test this are now, I believe, in
existence; the number of wells sunk in the chalk being so
considerable, and the quantity of water which they yield so well
known.
But this water, so admirable as regards freedom from mechanical
impurity, labours under the disadvantage of being rendered very hard
by the carbonate of lime which it holds in solution. The chalk-water
in the neighbourhood of Watford contains about seventeen grains of
carbonate of lime per gallon. This, in the old terminology, used to
be called seventeen degrees of hardness. This hard water is bad for
tea, bad for washing, and it furs our boilers, because the lime held
in solution is precipitated by boiling. If the water be used cold,
its hardness must be neutralised at the expense of soap, before it
will give a lather. These are serious objections to the use of
chalk-water in London. But they are successfully met by the fact that
such water can be softened inexpensively, and on a grand scale. I had
long known the method of softening water called Clark's process, but
not until recently, under the guidance of Mr. Homersham, did I see
proof of its larger applications. The chalk-water is softened for the
supply of the city of Canterbury; and at the Chiltern Hills it is
softened for the supply of Tring and Aylesbury. Caterham also enjoys
the luxury.
I have visited all these places, and made myself acquainted with the
works. At Canterbury there are three reservoirs covered in and
protected, by a concrete roof and layers of pebbles, both from the
summer's heat and the winter's cold. Each reservoir holds 120,000
gallons of water. Adjacent to these reservoirs are others containing
pure slaked lime--the so-called 'cream of lime.' These being filled
with water, the lime and water are thoroughly mixed by air forced by
an engine through apertures in the bottom of the reservoir. The water
soon dissolves all the lime it is capable of dissolving. The
mechanically suspended lime is then allowed to subside to the bottom,
leaving a perfectly transparent lime-water behind.
The softening process is this: Into one of the empty reservoirs is
introduced a certain quantity of the clear lime-water, and after this
about nine times the quantity of the chalk-water. The transparency
immediately disappears--the mixture of the two clear liquids becoming
thickly turbid, through the precipitation of carbonate of lime. The
precipitate is crystalline and heavy, and in about twelve hours a
layer of pure white carbonate of lime is formed at the bottom of the
reservoir, with a water of extraordinary beauty and purity overhead. A
few days ago I pitched some halfpence into a reservoir sixteen feet
deep at the Chiltern Hills. This depth hardly dimmed the coin. Had I
cast in a pin, it could have been seen at the bottom. By this process
of softening, the water is reduced from about seventeen degrees of
hardness, to three degrees of hardness. It yields a lather
immediately. Its temperature is constant throughout the year. In the
hottest summer it is cool, its temperature being twenty degrees above
the freezing point; and it does not freeze in winter if conveyed in
proper pipes. The reservoirs are covered; a leaf cannot blow into
them, and no surface contamination can reach the water. It passes
direct from the main into the house tap; no cisterns are employed, and
the supply is always fresh and pure. This is the kind of water which
is supplied to the fortunate people of Tring, Caterham, and
Canterbury.
*****
The foregoing article, as far as it relates to the theory which
ascribes epidemic disease to the development of low parasitic life
within the human life, was embodied in a discourse delivered before
the Royal Institution in January 1870. In June 1871, after a brief
reference to the polarisation of light by cloudy matter, I ventured to
recur to the subject in these terms: What is the practical use of
these curiosities? If we exclude the interest attached to the
observation of new facts, and the enhancement of that interest through
the knowledge that facts often become the exponents of laws, these
curiosities are in themselves worth little. They will not enable us
to add to our stock of food, or drink, or clothes, or jewellery. But
though thus shorn of all usefulness in themselves, they may, by
carrying thought into places which it would not otherwise have
entered, become the antecedents of practical consequences. In
looking, for example, at our illuminated dust, we may ask ourselves
what it is. How does it act, not upon a beam of light, but upon our
own bodies? The question then assumes a practical character. We find
on examination that this dust is mainly organic matter--in part
living, in part dead. There are among it particles of ground straw,
torn rags, smoke, the pollen of flowers, the spores of fungi, and the
germs of other things. But what have they to do with the animal
economy? Let me give you an illustration to which my attention has
been lately drawn by Mr. George Henry Lewes, who writes to me thus:
'I wish to direct your attention to the experiments of von
Recklingshausen should you happen not to know them. They are striking
confirmations of what you say of dust and disease. Last spring, when
I was at his laboratory in Wuerzburg, I examined with him blood that
had been three weeks, a month, and five weeks, out of the body,
preserved in little porcelain cups under glass shades. This blood was
living and growing. Not only were the Amoeba-like movements of the
white corpuscles present, but there were abundant evidences of the
growth and development of the corpuscles. (I also saw a frog's heart
still pulsating which had been removed from the body I forget how many
days, but certainly more than a week). There were other examples of
the same persistent vitality, or absence of putrefaction. Von
Recklingshausen did not attribute this to the absence of germs--germs
were not mentioned by him; but when I asked him how he represented the
thing to himself, he said the whole mystery of his operation consisted
in keeping the blood _free from dirt_. The instruments employed were
raised to a red heat just before use; the thread was silver thread and
was similarly treated; and the porcelain cups, though not kept free
from air, were kept free from currents. He said he often had
failures, and these he attributed to particles of dust having escaped
his precautions.'
Professor Lister, who has founded upon the removal or destruction of
this 'dirt' momentous improvements in surgery, tells us the effect of
its introduction into the blood of wounds. The blood would putrefy
and become fetid; and when you examine more closely what putrefaction
means, you find the putrefying substance swarming with infusorial
life, the germs of which have been derived from the atmospheric dust.
We are now assuredly in the midst of practical matters; and with your
permission I will refer once more to a question which has recently
occupied a good deal of public attention. As regards the lowest forms
of life, the world is divided, and has for a long time been divided,
into two parties, the one affirming that we have only to submit
absolutely dead matter to certain physical conditions, to evolve from
it living things; the other (without wishing to set bounds to the
power of matter) affirming that, in our day, life has never been found
to arise independently of pre-existing life. I belong to the party
which claims life as a derivative of life. The question has two
factors--the evidence, and the mind that judges of the evidence; and
it may be purely a mental set or bias on my part that causes me
throughout this long discussion, to see, on the one side, dubious
facts and defective logic, and on the other side firm reasoning and a
knowledge of what rigid experimental enquiry demands. But, judged of
practically, what, again, has the question of Spontaneous Generation
to do with us? Let us see. There are numerous diseases of men and
animals that are demonstrably the products of parasitic life, and such
diseases may take the most terrible epidemic forms, as in the case of
the silkworms of France, referred to at an earlier part of this
article. Now it is in the highest degree important to know whether
the parasites in question are spontaneously developed, or whether they
have been wafted from without to those afflicted with the disease. The
means of prevention, if not of cure, would be widely different in the
two cases.
But this is not all. Besides these universally admitted cases, there
is the broad theory, now broached and daily growing in strength and
clearness--daily, indeed, gaining more and more of assent from the
most successful workers and profound thinkers of the medical
profession itself--the theory, namely, that contagious disease,
generally, is of this parasitic character. Had I any cause to regret
having introduced this theory to your notice more than a year ago,
that regret should now be expressed. I would certainly renounce in
your presence whatever leaning towards the germ theory my words might
then have betrayed. But since the time referred to nothing has
occurred to shake my conviction of the truth of the theory. Let me
briefly state the grounds on which its supporters rely. From their
respective viruses you may plant typhoid fever, scarlatina, or
small-pox. What is the crop that arises from this husbandry? As
surely as a thistle rises from a thistle seed, as surely as the fig
comes from the fig, the grape from the grape, the thorn from the
thorn, so surely does the typhoid virus increase and multiply into
typhoid fever, the scarlatina virus into scarlatina, the small-pox
virus into small-pox. What is the conclusion that suggests itself
here? It is this: That the thing which we vaguely call a virus is to
all intents and purposes a seed. Excluding the notion of vitality, in
the whole range of chemical science you cannot point to an action
which illustrates this perfect parallelism with the phenomena of
life--this demonstrated power of self-multiplication and reproduction.
The germ theory alone accounts for the phenomena.
In cases of epidemic disease, it is not on bad air or foul drains that
the attention of the physician of the future will primarily be fixed,
but upon disease germs, which no bad air or foul drains can create,
but which may be pushed by foul air into virulent energy of
reproduction. You may think I am treading on dangerous ground, that I
am putting forth views that may interfere with salutary practice. No
such thing. If you wish to learn the impotence of medical practice in
dealing with contagious diseases, you have only to refer to the
Harveian oration for 1871, by Sir William Gull. Such diseases defy
the physician. They must run their course, and the utmost that can be
done for them is careful nursing. And this, though I do not specially
insist upon it, would favour the idea of their vital origin. For if
the seeds of contagious disease be themselves living things, it may be
difficult to destroy either them or their progeny, without involving
their living habitat in the same destruction.