Now the special interest of this new line of investigation I have been pursuing turns largely on the fact that this particular bacillus, which is not uncommon in the river Thames, is by no means a very sensitive one to light, as compared with several others known to me. For if such a form can be so easily destroyed in a few hours by the light from an April sky passing through several inches of water and two sheets of glass, we may fairly conclude that more sensitive forms are easily destroyed in the river, exposed to the rays of a summer sun during the long days of June, July and August. As matter of fact-and the fact has been confirmed by many other observations-I found that in spite of the high temperature of the past summer, which we should expect to favour the development of bacteria; and in spite of the river being low, and presumably more concentrated as a food-solution for bacteria; and, further, in spite of the fair expectation that, per unit of volume, the water ought to contain more bacteria than during the cold months of October, November and December, when the river is more diluted, and so on; the number of bacteria per cubic centimeter is decidedly and markedly less in the summer than in the winter months! This is very clearly shown by the statistical curves I now throw on the screen. [Curves of average number of bacteria per 1 cubic centimeter of Thames water in August, October and December, 1893.] Now I am perfectly aware that it has been the custom to regard this well-known fact as due to a series of causes of quite different kinds, the action of which may or may not co-operate in bringing about the variations in the quantities of bacteria per unit of volume in such a river as the Thames, but I submit to you whether, in view of the new facts I have elicited, it is not at least highly probable that the increased intensity of the light, acting during a longer period through the summer days, is a very powerful agent in keeping down the numbers of these bacterial and fungoid organisms in the river. It must be remembered that in my experiments, although I get such pronounced positive results wherever I employ water enclosed in glass vessels as the screen, I certainly do not get anything like the effects that the same exposures give if I dispense with the glass of the containing vessels, mirrors, &c.; for even a thin plate of glass is a decided obstruction to the rays at the violet end of the spectrum, and so I have to record positive results considerably below what I should get if the light from the sun and blue sky reached the organisms through the medium of water only. In the experiments I am now continuing, no glass whatever is employed, and the light is not allowed to traverse or be reflected from any but quartz or metal surfaces. Unfortunately, we are as yet but scantily informed as to how far the blue-violet rays penetrate into deep water, but experiments by Regnard, Fol, Forel and others have shown that they do penetrate to a considerable depth. Fol, for instance, showed that some light gets down as far as 400 meters, and Forel got effects with photographic paper at 45 to 100 meters in the Lake of Geneva, and so on, depths quite sufficient for my purposes, though I hope that more accurate and extended information will yet be obtained on the subject. Some consequences of this view of the destruction of bacteria in water by light are of the utmost importance. For instance, we can understand how the typhoid bacillus, if it falls into turbid dirty water in the summer, may multiply at the high temperature and at the expense of the food-materials dissolved from the organic matters in suspension, and this at its pleasure, so to speak, because the suspended particles of matter, to which the turbidity is due, favour it in (1) supplying it with food, (2) absorbing heat and helping to raise the temperature of the water, and (3) impeding the penetration of the destructive light-rays. The results of the investigation also suggest explanations for many other facts which have hitherto been unexplained. Thus Pasteur and Miquel pointed out some time ago that the germs floating about in the air are for the most part dead! This we can explain by the bactericidal action of the sun's rays, just as we can also probably explain the freedom from germs of the Alps. Again, Martinaud has shown that certain yeasts which normally vegetate on the exterior of ripening grapes, are destroyed if the sunshine is very intense; and Giunti has stated that the ingress of sunlight hinders acetic fermentation, a process which depends on the life-processes of a well-known bacterium. I have myself observed many cases where the free access to light is inimical to the germination and development of fungi of various kinds, and Elfving has recently studied very thoroughly the action of light on a common mould-fungus with astonishing results, quite intelligible in the light of the foregoing investigation. These matters are of more significance in connection with the spread of the potato and other diseases in dull warm weather than I have time to explain here; and probably have a wide bearing on the deterioration of forest and agricultural soils exposed to the sun, as well as on many questions of greenhouse practice too numerous to even mention. They also bear on the question of sun-baths, and the whole hygiene of sunshine treatment; as well as sun-burn, "tanning," snow-blindness, &c. But still more startling probabilities must be looked at, though I have brought my lecture now to a point where I must remember that your patience in listening to me should not be abused. We have seen that in my experiments certain colour-screens are efficacious in so cutting off the access of the destructive rays, that the protected germs, bacilli, fungus-spores, &c., can germinate and develop as easily as if no light at all was playing on them. It struck me during the progress of these experiments that just such colour-screens are very common in Nature, in cases where just such spores and tender growing cells are compelled to begin or carry on their vegetative processes in the light. This led me a short time ago to publish the following opinions based on the facts even then to hand:-It seems likely that pollen-grains, many fungus-spores and a large number of such organisms as are exposed to light, are provided with the colour screens they possess, and which screens are usually red or orange, or some shade such as cuts out the blue-violet rays, as an adaptive protection against the injurious rays of light. It is but an extension of this to see in the green chlorophyll-screen of all our ordinary plants in part a protection against the blue-violet rays of ordinary sunlight, the ingress of which to the cell-contents would bring about destructive changes of the order discussed in this lecture; but we must not forget that the chlorophyll-apparatus is more complex than this, and is essential to the process of carbon assimilation, absorbing and making use of the energy derived from the red-orange rays. In conclusion, it is impossible to put forward in a single lecture all the results obtained, and still less the bearings of these results and the experiments now being continued. I can merely say that there is evidence to show that the slow and continued action of even comparatively low intensities of light so act on these bacteria I am working with that even where they are not killed, but only partially injured by the inimical rays, their behaviour is so altered that the resulting growths are perceptibly different from those of the same organisms not exposed to light, that their powers of fermenting organic substances are interfered with, and that various profound morphological and physiological changes are induced in them. The bearings of these matters-which are very complex, and the investigation of which is full of peculiar difficulties moreover, are so important in regard to various questions concerning fermentation, the germ-theory of disease and other departments of bacteriology, that I have no hesitation in saying that no subject more vital to the interests of mankind exists in the whole domain of biological science. [H. M. W.] ANNUAL MEETING, Tuesday, May 1, 1894. SIR JAMES CRICHTON-BROWNE, M.D. LL.D. F.R.S. Treasurer and The Annual Report of the Committee of Visitors for the year 1893, testifying to the continued prosperity and efficient management of the Institution, was read and adopted. The Real and Funded Property now amounts to above 102,000l. entirely derived from the Contributions and Donations of the Members and of others appreciating the value of the work of the Institution. Sixty-two new Members were elected in 1893. Sixty-three Lectures and Nineteen Evening Discourses were delivered in 1893. The Books and Pamphlets presented in 1893 amounted to about 250 volumes, making, with 584 volumes (including Periodicals bound) purchased by the Managers, a total of 834 volumes added to the Library in the year. Thanks were voted to the President, Treasurer, and the Honorary Secretary, to the Committees of Managers and Visitors, and to the Professors, for their valuable services to the Institution during the past year. The following Gentlemen were unanimously elected as Officers for the ensuing year: PRESIDENT-The Duke of Northumberland, K.G. D.C.L. LL.D. MANAGERS. Sir Frederick Abel, Bart. K.C.B. D.C.L. LL.D. Captain W. de W. Abney, C.B. D.C.L. F.R.S. Edward Frankland, Esq. D.C.L. LL.D. F.R.S. William Huggins, Esq. D.C.L. LL.D. F.R.S. Hugo Müller, Esq. Ph.D. F.R.S. Sir Andrew Noble, K.C.B. F.R.S. M. Inst. C.E. VISITORS. Charles Edward Beevor, M.D. F.R.C.P. Joseph Gordon Gordon, Esq. F.C.S. Donald William Charles Hood, M.D. F.R.C.P. Lachlan Mackintosh Rate, Esq. M.A. Sir Owen Roberts, M.A. D.C.L. F.S.A. |