Part 6

Huxley has said "science is nothing but trained and organised common sense," and it is in this spirit that we must endeavour to make use of the discoveries which have been made in the prevention of disease, in which the science of bacteriology has played so great and important a part.

SUNSHINE AND LIFE

It was nearly a century ago that a German physician incidentally wrote, "Our houses, hospitals, and infirmaries will, without doubt, some day be like hot-houses, so arranged that the light, even that of the moon and stars, is permitted to penetrate without let or hindrance." This was spoken long before the world of micro-organisms had been discovered, but curiously has found an echo in the writings of a distinguished bacteriological chemist in recent years. "Laissons donc entrer largement partout l'air et le soleil," writes M. Duclaux; "c'est là une maxime bien ancienne, mais si les mots sont vieux l'idée qu'ils revêtent est nouvelle." The interpretation of this ancient maxim is indeed very modern, and we must turn to the investigations made within the past few years to learn with what justification M. Duclaux thus expresses himself, for it is only comparatively recently that we have learnt the novel fact that sunshine, whilst essential to green plant life, is by no means indispensable to the most primitive forms of vegetable existence with which we are acquainted, i.e. bacteria. In fact, we have found out that if we wish to keep our microbial nursery in a healthy, flourishing condition, we must carefully banish all sources of light from our cultivations, and that a dark cupboard is one of the essential requisites of a bacteriological laboratory.

That light had a deleterious effect upon micro-organisms was first discovered in this country by Messrs. Downes and Blunt, and their investigations led Professor Tyndall to carry out some experiments on the Alps, in which he showed that flasks containing nutritive solutions and infected with bacteria when exposed in the sunshine for twenty-four hours remained unaltered, whilst similar vessels kept in the shade became turbid, showing that in these the growth of bacteria had not been arrested. In these experiments mixtures of micro-organisms were employed, and the interest of the French investigations which followed lies in the use of particular microbes--notably the anthrax bacillus and its spores, Roux demonstrating very conclusively that the bacillar form was far more sensitive to light than the spore form, while Momont, in a classical series of experiments, not only fully confirmed these observations, but showed also that the intensity of the action of light depends to a very large extent on the environment of the organism. Thus, if broth containing anthrax bacilli is placed in the sunshine, the latter are destroyed in from two to two and a half hours, whilst if blood containing these organisms is similarly exposed, their destruction is only effected after from twelve to fourteen hours of sunshine. This difference in resistance to insolation was also observed in the case of dried blood and broth respectively--eight hours' exposure killing the bacilli in the former, whilst five hours sufficed in the latter.

In the interior of some bacilli there appears a round or oval body, having a very bright and shining lustre, which is known as a spore, and plays a most important part in the propagation of many kinds of bacilli. These spores are capable of resisting many hardships, which would be immediately fatal to the parent bacilli from which they have sprung.

This is an instance of the apparent idiosyncrasies possessed by micro-organisms, which render their study at once so fascinating and so difficult, and it is through being thus constantly confronted with what, in our ignorance, we mentally designate as "whims," that we can hardly resist the impression of these tiny forms of life being endowed with individual powers of discernment and discrimination. Indeed, these powers of selection and judgment are in certain cases so delicately adjusted that in some of the modern chemical laboratories micro-organisms have become indispensable adjuncts, and by their means new substances have been prepared and fresh contributions made to the science of chemistry.

Momont is not able to give any satisfactory explanation of this different behaviour of the anthrax bacilli in these two media, but goes on to show that yet another factor plays an important part during insolation.

In the above experiments air was allowed to gain access to the vessels containing the broth, but if the precaution be taken of first removing the air and then exposing them to the sunshine, a very different result was obtained, for instead of the anthrax bacilli dying in from two to two and a half hours, they were found to be still alive after fifty hours' insolation. There appears, therefore, to be no doubt that sunshine in some way or other endows atmospheric oxygen with destructive power over the living protoplasm of the bacterial cells; indeed, there is considerable reason to believe that the bactericidal effect is due to the generation of peroxide of hydrogen, which is well known to possess powerfully antiseptic properties.

Numerous investigations have been also made to determine whether all the rays of the spectrum are equally responsible for the bactericidal action of light.

Geisler's work in St. Petersburg is especially instructive in this respect, for by decomposing with a prism the sun's light, as well as that emitted by a 1,000-candle-power electric lamp into their constituent rays, he was able to compare the different effects produced by the separate individual rays of both these sources of light.

The organism selected was the typhoid bacillus, and it was found that its growth was retarded in all parts of the two spectra excepting in the red, and that the intensity of the retardation was increased in passing from the red towards the ultraviolet end of the spectrum, where it was most pronounced of all.

But whereas from two to three hours of sunshine were sufficient to produce a most markedly deleterious effect upon the typhoid bacillus, a similar result was only obtained by six hours' exposure to the electric light.

Dr. Kirstein, of the University of Giessen, in the course of some experiments he made to ascertain how long different varieties of bacteria can exist when they obtain access to the air in the form of fine spray, and subsequently, as happens under ordinary circumstances, get dried up, noted also the effect upon their vitality of exposure in daylight and darkness respectively. For this purpose the apparatus in which the experiments were carried out was in some cases kept in a dark cellar, whilst in others it was left standing in the laboratory in ordinary daylight.

Delicate bacteria, such as the fowl-cholera bacillus, it was found, could not survive exposure to daylight in this dried-up condition for more than ten hours, but when they were put in the dark their lease of life was prolonged for more than twice that length of time; whilst as regards varieties of tougher constitution, such as diphtheria and tubercle bacilli, whose initial vitality was very considerably greater under these adverse circumstances, confinement in the cellar enabled them to exist more than four times as long as they were able to in the healthy atmosphere of the well-lighted laboratory.

Dr. Onorato, of the University of Genoa, has recently shown, also, that influenza bacilli are entirely destroyed after the sun has been shining on them continuously for three and a half hours.

Such facts indicate how essential to health is plenty of light in our dwelling-rooms, and how important it is that in the designing of houses the trapping of the maximum amount of sunshine should be very carefully considered. Architects might indeed with advantage be compelled to include in their qualifications a knowledge of the fundamental facts of sanitary science. The fashion of shutting the sunshine out by barriers of blinds and curtains drawn across the windows, a practice which seems to be almost entirely independent of the habitual gloom of the surroundings or general scarcity of sunshine, might possibly be modified were it but known that by thus excluding light we are conferring an inestimable benefit upon the members of the microbial community, which may at any moment comprise some of the subtlest and most dangerous antagonists with which we have to reckon in the struggle for existence.

From a hygienic point of view, also, the question of the potency of sunshine in regard to the bacteria present in water is both important and interesting, for it is to water at the present time that we look for the dissemination of some of the most dreaded zymotic diseases.

Comparatively little has been done in this direction, but those results which have been obtained are exceedingly suggestive. Professor Buchner has published some preliminary experiments which he made with particular micro-organisms. In these investigations boiled tap-water was used to ensure the absence of all bacteria except those which were subsequently introduced, and, whilst some of the vessels were exposed to the sunshine, others were simultaneously preserved in the dark. It was found that typhoid, cholera, and various other bacilli were most deleteriously affected by insolation. Perhaps an example will best serve to illustrate the nature of the results obtained. Some boiled water contained in a flask was inoculated with an immense number of a bacillus, closely resembling the typhoid organism, normally present in the body and frequently found in water, the bacillus coli communis. So many were introduced that nearly one hundred thousand individuals were present in every twenty drops of the water. This flask then, containing water so densely sown with microbes, was placed in the sunshine for one hour, whilst another and similar flask was kept during the same time in the dark. On being subsequently examined it was ascertained that whereas a slight increase in the number of bacilli had taken place in the "dark" flask, in the insolated flask absolutely no living organisms whatever were present.

Professor Percy Frankland has also investigated the action of sunshine on micro-organisms in water, and in one of his reports to the Water Research Committee of the Royal Society an account is given of the effect of insolation on the vitality of the spores of anthrax in Thames water. These experiments show again what an important influence the surroundings of the organism have on the bactericidal potency of the sun's rays, for the remarkable fact was established that when immersed in water anthrax spores are far less prejudicially affected by sunlight than when exposed in ordinary culture materials such as broth or gelatine. Thus it was only after one hundred and fifty-one hours' insolation in Thames water that these spores were entirely destroyed, whilst a few hours' exposure in the usual culture media is generally sufficient for their annihilation. In water not subjected to insolation anthrax spores were found to retain their vitality for several months.

In case the reader should be tempted to compare these results with 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 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.

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.