those obtained by Buchner, it must be borne in mind that whereas those
experiments were made with _bacilli_, these were directed to determine
the behaviour of _spores_ in water, which are some of the hardiest
forms of living matter with which we are acquainted. This alone would
sufficiently explain the results obtained, whilst each variety of
microbe may be, and doubtless is, differently affected during
insolation.
We know now that a remarkable improvement takes place in the bacterial
condition of water during its prolonged storage in reservoirs, and
although, no doubt, the processes of sedimentation which have been
shown to take place during this period of repose are to a large extent
responsible for the diminution in the number of bacteria present, yet
it is also highly probable that insolation assists considerably in
this improvement, at any rate, in the upper layers of the water. As
the depth of the water increases the action of light is necessarily
diminished. Indeed, exact experiments conducted in the Lake of Geneva
to ascertain by means of photographic plates the depth to which the
sun's rays penetrate showed that they did not reach beyond five
hundred and fifty-three feet, at which depth the intensity of the
light is equal to that which is ordinarily observed on a clear but
moonless night, so that long before that their bactericidal potency
would cease.
It is the more important that this limit to the powers of sunshine in
water should be duly recognised, inasmuch as solar enthusiasts, when
first the fact became known, rashly jumped at the convenient
hypothesis, based on very slender experimental evidence, that the
sun's rays were possessed of such omniscient power to slay microbes,
that they might safely be relied upon to banish all noxious organisms
from our streams, and that local authorities might therefore
comfortably and without any qualms of conscience turn sewage into our
rivers and so dispense with the cost and labour of its treatment and
purification.
This was actually suggested in a proposal made for dealing with the
sewage of the city of Cologne. Fortunately further investigations have
removed these most erroneous and dangerous ideas; and whilst all due
credit may be given to sunshine for what it really does accomplish in
the destruction of bacteria in water, there is now no doubt as to its
potency being confined to the superficial layers of water.
Perhaps Dr. Procacci's experiments will most clearly convey some idea
of this limitation, for he made a special study of this particular
phenomenon. Some drain water, containing, of course, an abundance of
microbial life, was placed in cylindrical glass vessels, and only the
perpendicular rays of the sun were allowed to play upon it. The column
of water was about two feet high, and whilst a bacteriological
examination at the commencement of the research showed that about two
thousand microbes were present in every twenty drops of water taken
from the surface, centre, and bottom of the vessel respectively, after
three hours' sunshine only nine and ten were found in the surface and
centre portions of the water, whilst at the bottom the numbers
remained practically unchanged. Professor Buchner, of Munich,
demonstrated the same impotence of the sun's rays to destroy bacteria
much beneath the surface of water, in some ingenious experiments he
made in the Starnberger See, near Munich. He lowered glass dishes
containing jelly thickly sown with typhoid bacilli to different depths
in the water during bright sunshine; those kept at a depth of about
five feet subsequently showed no sign of life, whilst those immersed
about ten feet developed abundant growths; in both cases the exposure
was prolonged over four and a half hours.
In our own rivers Thames and Lea frequently about twenty times more
microbes have been found in the winter than in the summer months, but
it would be extremely rash to therefore infer that the comparative
poverty of bacterial life was due to the greater potency of the sun's
rays in the summer than in the winter. Doubtless it may contribute to
this beneficial result; but we know as a matter of fact that, in the
summer, these rivers receive a large proportion of spring water, which
is comparatively poor in microbes, and that this factor also must not
be ignored in discussing the improved bacterial quality of these
waters at this season of the year.
Another point which must be taken into consideration in regard to the
effective insolation of water is its chemical composition, for it has
been shown[5] that the action of sunshine in destroying germs in water
is very considerably increased when common salt is added to the water,
and this opens up a wide field for experimental inquiry before we can
accept sunshine as a reliable agent in the purification of water.
[5] PERCY FRANKLAND, _Our Secret Friends and Foes_, 4th
edition, p. 188.
Again, we must remember that a great deal depends upon the condition
of the microbe itself. If it is present in the spore or hardy form,
then considerably longer will be required for its annihilation. This
fact has been abundantly shown in the case of anthrax, which in the
condition of spores will retain its vitality in water flooded with
sunshine for considerably upwards of a hundred hours, the bacilli
being far more easily destroyed. We must also bear in mind that the
individual vitality of the microbe is an important factor in
determining its chance of survival; if it is in a healthy, vigorous
condition, it will resist the lethal action of sunshine for
considerably longer than when its vitality has been already reduced by
adverse surroundings.
It is, therefore, sufficiently obvious that the power of insolation to
bacterially purify water is by no means easy of estimation, and that
numerous and very varied factors have to be taken into account when we
attempt to endow it with any measure of practical hygienic importance.
In connection with the vitality of anthrax germs in water, which has
afforded material for so many laboratory investigations, it is of
interest to consider what chance exists of anthrax being communicated
by water. Until a few years ago, as far as I am aware, no instance had
been recorded of anthrax having been actually communicated by water,
until an outbreak of anthrax on a farm in the south of Russia was
distinctly traced by a skilled bacteriologist to the use of water from
a particular well, in the sediment of which the bacillus of anthrax
was discovered.
Anthrax bacilli have also been detected in the water of the River
Illinois in the vicinity of Chicago, one of the chief sources of
pollution of which is the slaughtering of cattle and the discharge of
their offal into the river.
The likelihood of such contamination taking place through the drainage
of soil makes it of importance to ascertain what may become of the
bacilli of anthrax derived from the bodies of animals which have died
of this disease, and whose carcasses have been buried and not burnt.
The anthrax bacillus cannot produce the hardy spore form within the
bodies of animals, but it does outside. Now it has been shown that the
bacilli of anthrax taken from the blood of an animal dead of anthrax
are destroyed rapidly in ordinary River Thames water, for example, but
that if the temperature of the water to which they gain access is
somewhat higher than usual, such bacilli are able to sporulate or
produce spores in the water, and in that hardy form can retain their
vitality and virulence for several months.
That anthrax bacilli can produce spores in water under certain
conditions has not hitherto been dwelt upon in discussing the question
of their vitality in water, and it is of obvious importance in
connection with the action of sunshine on anthrax germs in water,
knowing as we now do the very different manner in which the spores and
bacilli respectively behave when under the influence of the sun's
rays.
It was not, perhaps, unnatural that rash assumptions as to the
efficacy of sunshine should have been readily accepted when such
remarkable feats performed on microbes by sunshine were being
continually put forward.
Thus it has been found that insolation, even when it does not destroy,
may effect profound changes in the physiological character of certain
micro-organisms.
Dr. Lohmann, of Rostock, discovered that some hours' exposure to
bright sunshine entirely destroys yeast cells, whilst even feeble and
intermittent sunshine is capable of paralysing them, and that they
only recover their vitality when removed from this obnoxious
influence. This recuperative power is not, however, shared equally by
all varieties of yeast, some possessing it in a far greater degree
than others. Dr. Lohmann also found that yeast cells, after being
exposed to sunshine, assumed a shrunken and distorted appearance,
showing that insolation had produced a striking physiological effect
upon the structure of these cells.
Professor Hansen published some years ago a most interesting memoir on
some of the characteristic features of the moulds which are to be
found on manure heaps, in which he records how light exerts a very
important influence on the manner in which the spore or fruit of these
lowly vegetables is set free or distributed. All the various phases in
the fructification process of some of these moulds were carefully
watched by Dr. Hansen. He kept his caged specimens near a window with
an eastern aspect, and he states that in the first instance the stalks
inclined towards the light, but that afterwards they assumed an
upright position. Darkness was nearly always chosen for the liberation
of the spores, but in a few instances a small number were released
during the daytime, and it was noticed that when this did occur they
were invariably discharged on the side away from the source of light.
In various other ways he confirmed this interesting observation, and
found that the fruit of the mould was invariably discharged in the
opposite direction to that in which the stalk had previously inclined
under the influence of light. The force with which the spores were
discharged varied very considerably, sometimes being cast to a
distance of four inches or more from the stalk, and sometimes being
found close to and even on the stalk.
The manner in which sunshine may also modify the pigment-producing
powers of micro-organisms is remarkable.
Many microbes are able to elaborate when grown on various culture
media, such as gelatine or slices of potato, most brilliant and
beautiful pigments ranging from intense blood-red to the most delicate
shades of pink, and embracing every gradation of yellow, as well as
browns, greens, and violets. Now it has been found that some of these
pigment-producing bacteria, when exposed to sunshine on these
nutritive materials, fail to exhibit their characteristic colour,
although the duration of insolation may not have sufficed to destroy
their actual vitality. One of these organisms originally obtained from
water has been specially studied in this respect by M. Laurent. If
slices of potato are streaked with a small number of this particular
bacillus (_bacille rouge de Kiel_) a magnificent patch of blood-red
colour makes its appearance in the course of a day or two, but if, on
the other hand, similar slices of potato are exposed to three hours'
sunshine, a colourless growth subsequently develops, except where here
and there a few isolated spots of pale pink are visible. When the
insolation is prolonged for five hours nothing whatever appears on the
potato, the bacilli having been entirely destroyed. But this is not
all. M. Laurent found that if he took some of the colourless growth
and inoculated it on to potatoes he obtained again, but without
insolation, a colourless vegetation--in fact, three hours' insolation
had so modified the physiological character of the bacillus that _a
new race had been generated, a race deprived of its power of producing
this red pigment_. In what numerous directions the character of
microbes may be and are being modified, even by simple exposure to
sunshine, opens up a wide field for speculation and research, whilst
the tractability of these minute and most primitive forms of life, if
we only approach their education with sufficient insight and patience,
may enable us to make them serve where they now are masters.
The remarkable discoveries on the modification of the
disease-producing properties of certain bacteria by sunshine may
perhaps encourage the idea that we are making some progress towards
the attainment of this desirable millennium. That diminution of the
virulence or disease-producing power of such deadly microbes as those
of cholera, anthrax, and tuberculosis can be brought about through
simple exposure to the sun's rays seems almost inconceivable, yet it
has been discovered that by placing the cholera bacillus, for example,
in the sunshine its virulent character undergoes such a profound
modification that it is actually reduced to the condition of a
vaccine, and may be employed to protect animals from infection with
its still virulent brethren. Yet this is what has been undoubtedly
shown by Dr. Palermo in very carefully conducted investigations. He
was, moreover, able to indicate, within a very narrow margin, the
precise amount of insolation necessary to bring about this result: for
if the cholera cultures were only exposed for three hours, their toxic
properties were not reduced to the condition of vaccine; but if the
insolation was continued for three and a half hours up to four and a
half hours, they became endowed with the requisite immunising
properties, and animals treated first with the so-called
sunshine-cholera-vaccine were able subsequently to withstand otherwise
fatal doses of virulent cholera cultures. Dr. Palermo also found that,
besides producing this subtle modification in the character of cholera
bacilli, sunshine exerted a remarkable physiological change in these
organisms, for when examined under the microscope they no longer
exhibited their typical activity, having been deprived of all powers
of movement, whilst those kept during the same length of time in the
dark had not abated one jot of their customary mobility.
But sunshine not only controls in this wonderful manner the action of
the living bacillus, but it also operates upon the products elaborated
by disease organisms. Thus the microbe producing lock-jaw or tetanus
may be grown in broth, and the latter may be subsequently passed
through a porcelain or a Berkefeld filter, so that the resulting
liquid is entirely deprived of all germ life. This tetanus-filtrate,
as it is called, is endowed with very powerful toxic properties, and
it will retain its lethal action even when kept for upwards of three
hundred days, providing it is screened from all light; but place such
filtrates in diffused light, and they lose their poisonous properties,
requiring, however, upwards of ten weeks to become entirely harmless;
if, on the other hand, they be exposed to sunshine, they are
completely deprived of their toxic character in from fifteen to
eighteen hours. Again, as little as five hours' sunshine is sufficient
to greatly modify the toxic action of diphtheria cultures. It is of
interest also to note that even the venom of the rattlesnake, that
most potent of all poisons, cannot emerge unscathed from an exposure
to sunshine maintained during a fortnight.
Interesting as all these isolated observations are, they indicate what
an immense amount yet remains to be done before we can hope to have
any connected conception of the mechanism, so to speak, of insolation.
At present there is too large an allowance, which we are compelled to
make, for the unknown to permit of our adequately manipulating this
marvellous agency in relation to bacteriological problems. But who
shall say what part has been, and is being still, played by sunshine
in determining the individual character of microbes, operating as it
has done from time immemorial upon countless generations of these
minute germs of life?
The problem of insolation has been attacked from an entirely novel
point of view by Dr. Masella, who has endeavoured to find out whether
sunshine plays any part in the predisposition of animal life to
infection.
Now sunshine has long been credited with possessing therapeutic
powers, and, indeed, traditions of cures effected by the ancients by
means of insolation have been treasured up and handed down to the
present day. Even as late as the beginning of the present century we
may read of a French physician seriously recording his claim to have
cured a dropsical patient within two weeks by placing him daily for
several hours in the sunshine, and many medical journals of recent
years contain communications on the beneficial results derived from
the use of sunshine in the treatment of various diseases. It seems
curious, therefore, that whilst so much has been done to test the
action of light on disease microbes in _artificial_ surroundings, such
as are to be found in laboratory experiments, hardly any
investigations have been made to try and define more precisely how
sunshine may affect their pathogenic action within the animal system.
Dr. Masella's researches, undertaken with the express object of, if
possible, elucidating this question, are therefore of special interest
and importance.
The first series of experiments was carried out to ascertain whether
exposure to sunshine increases or reduces an animal's susceptibility
to particular diseases, those selected for investigation being typhoid
fever and cholera. For this purpose guinea-pigs were exposed to the
full rays of the sun during a period of from nine to fifteen hours for
two days, whilst other guinea-pigs, for the sake of comparison, were
not permitted to have more light than that obtainable in a stable
where only diffused light was admitted. Both these sets of animals
were subsequently infected with virulent cultures of cholera and
typhoid germs respectively, and were in neither case exposed to
sunshine. The results which Dr. Masella obtained were remarkable, for
he found that those animals which previous to infection had been
placed in the sunshine died more rapidly than those which had been
kept in the stable, and that the exposure to the sun's rays had so
increased their susceptibility to these diseases that they succumbed
to smaller doses, and doses, moreover, which did not prove fatal to
the other guinea-pigs. Still more striking was the part played by
insolation in the course of these diseases in animals exposed to
sunshine _after_ inoculation, for instead of dying in from fifteen to
twenty-four hours, they succumbed in from three to five hours.
Here, then, we find sunshine, in some mysterious manner not yet
understood, far from benefiting the animal and assisting it in
combating these diseases, actually contributing to the lethal action
of these bacteria. It has been asserted on the authority of some
medical men that in cases of small-pox recovery is rendered more easy
and rapid when light is excluded from the patient's room; whether Dr.
Masella's experiments will permit of any such interpretation being
placed upon them remains to be seen; they are, at any rate, extremely
suggestive.
That it is possible for temperature to have some determining influence
upon the course of certain diseases has been shown by O. Voges, who,
experimenting with a minute bacillus which he isolated from tumours
characteristic of a cattle disease very prevalent in South America,
found that although this bacillus was the undoubted _fons et origo_ of
the disease, he could not produce fatal results in animals if he kept
them in cold surroundings; only when the temperature was raised to
from 35-45 degrees Centigrade did the infected animals succumb. The
dependence of the activity and virulence of this micro-organism upon
temperature is also borne out in actual experience, the disease being
the more prevalent and the more fatal the hotter the climate of the
country.
It may be mentioned in passing that this bacillus has the distinction
of being the smallest yet discovered; the influenza bacillus hitherto
held the palm in this respect, but it must yield its position to its
more successful rival, for Voges states that when magnified about
fifteen hundred times it is only just discernible in the microscopic
field.
Even the smoke-laden atmosphere of our great cities, our leaden skies
and dreary fogs and mists, may after all, then, if we can only learn
to look at them from Dr. Masella's point of view, become a source of
benefit and a subject for congratulation; yet our inherent love of
light and sunshine would cause us willingly to hand over our murky
climate had we but the chance of obtaining in exchange that of any of
the sunny cities of the south. Moreover, in the case of tubercular
disease experience is daily impressing upon us the wisdom, and indeed
necessity, of absorbing as much sunshine as possible, and hence the
pilgrimage which is now recommended to Davos and other resorts where
invalids can get the maximum amount of bright sunshine. And not only
is this the outcome of practical experience, but De Renzi has shown by
actual experiment that sunshine acts beneficially in cases of
tuberculosis in animals. Thus, guinea-pigs were infected with
tuberculous material and exposed in glass boxes to the sun for five or
six hours daily, others being similarly infected but protected from
sunshine. The animals which had received the sunshine died in 24, 39,
52, and 89 days respectively, whilst those which had not been sunned
succumbed in from 29, 25, 26, and 41 days; or, in other words, De
Renzi found that insolation had very materially increased the infected
animals' power of coping with tuberculosis.
The part which sunshine plays, or may be made to play, in disease is
very obscure, but it would appear at least justifiable to assume that
it is an agent which further investigation may show we cannot afford
to disregard, contributing as it may to the production of a healthy
tone in the system, and thereby materially assisting the body to defy
the insidious attacks made upon it from without.
The so-called open-air treatment of consumption which has made such
giant strides in the last few years is an example of how, by
contributing to the general health of an individual, the powers for
resisting a localised disease may be so increased that the latter can,
in many cases, be thrown off altogether. In no country has more
progress been made in the establishment of institutions for the cure
of consumption on these lines than in Germany. At the end of the year
1899 there were forty-nine such institutions in Germany, with four
thousand beds; in a little more than twelve months later there were no
less than sixty such, with accommodation for altogether five thousand
patients. It is of interest to note that amongst the earliest of these
institutions to be founded was that erected and endowed by the famous
Badischen Anilin and Soda Fabrik Company, for the exclusive benefit of
those of their workpeople who were suffering from tuberculous disease.