Inaugural lecture on the possibility of extirpating malaria from certain localities by a new method / by Ronald Ross.

  • Ross, Ronald, Sir, 1857-1932.
Date:
1899
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Licence: Public Domain Mark

Credit: Inaugural lecture on the possibility of extirpating malaria from certain localities by a new method / by Ronald Ross. Source: Wellcome Collection.

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    Reprinted from the British Medical Journal, July 1st, 1899, INAUGURAL LECTURE ON THE POSSIBILITY OF EXTIRPATING MALARIA FROM CERTAIN LOCALITIES BY A NEW METHOD. By Major RONALD ROSS, D.P.H., M.R.C.S., Lecturer in Tropical Medicine, University College, Liverpool. I cannot help feeling that the Liverpool School of Tropical Medicine has been founded at a most opportune moment—at a moment when science has at last opened the way for an im¬ portant and interesting adventure—an adventure which is well within our power at least to attempt if not to succeed in : I refer to the experimental trial of a new method, indi¬ cated by recent discoveries, for the extirpation of malaria from certain limited areas. That malaria can often be removed by artificial means has long been proved by actual experience. It is a familiar fact— which I need not dwell upon—that the disease often disappears as the result of drainage and cultivation. *We have many ex¬ amples of this in Europe and America, and, indeed, in Eng¬ land itself, where tracts formerly malarious have now become quite or comparatively salubrious. Unfortunately, however, there are many malarious localities which we cannot drain and cultivate without a degree of ex¬ pense which it is impossible to incur ; while there are others, as I have myself experienced, where the most virulent malaria remains in spite of both cultivation and drainage. While, therefore, such successful examples as 1 have alluded to entitle us to admit the possibility of extirpation in some cases, we are forced to add that drainage is neither a sure nor always a practicable mode of dealing with the disease. As a matter of fact, the efficacy of drainage of the soil as regards malaria is merely the expression of a very familiar law : that this disease, like many others, is connected in some way with humidity ; when we remove humidity we often re¬ move malaria. But, nevertheless, drainage must be looked upon as being only an empirical and somewhat gross measure which has been employed by mankind in the absence of any more precise method of extirpation. For instance, in sweep¬ ing away all the superfluous waters of a given area, it is possible that we reduce its malaria only because we have hap¬ pened to remove together with those waters some small pond or puddle which was all the time the true source of the dis¬ ease, and which, had we been able to detect it before we could have removed at a hundredth part of the cost. Fortu¬ nately, we may now ask with some hope of receivin0, an answer whether science cannot put us in possession of a more accurate means of detecting the precise focus of malaria in such localities, and, after detection, of removing it. Unhappily, our efforts to obtain a more scientific frontier of defence against this disease have always hitherto been defeated by our ignorance as to the exact manner in which the infection is produced. For many years, indeed, we have t i , malarial fever is due to certain minute parasites of the blood; but how and where these parasites live in external Nature, and how and where they effect an entrance into our bodies we have not been able until lately to discover Hence, in formulating our epidemiology of the disease we were compelled to fall back upon mere conjectures. Knowing little more than the fact that malaria adheres to certain tracts of country, especially to humid tracts, we assumed that the germs exist at large in the soil, air, or water of such places ; that they 'propagate themselves in these elements ; that they are carried by winds from one spot to another; that they rise in mists and exhalations from the soil; that they infect us through the air we breathe or the water which we drink. On what facts were such notions founded ? on what exact reasoning ? on what precise experiments P On none at all. Vague conjectures, personal impressions, imperfect evi¬ dence, were the data on which we were forced to rely—we had none better. The parasites of malaria, so easily detected in the blood of patients, could nowhere be found in external Nature; we had questioned the winds and waters vainly for them; we therefore remained ignorant of how they attack us, and lived without defences against our invisible enemy. As in many other branches of science, so in respect to malaria, the experimental method of research now compels us to abandon notions based on less trustworthy modes of in¬ inquiry. In place of our former theories we now possess a clear knowledge of how and where the parasites of malaria live in external Nature, and how and where they enter us. They do not float free in the air or water, as we supposed; they do not rise in mists and exhalations from the soil; they live encased in the bodies of mosquitos, from which they pass into our blood at the moment when the insect inflicts her bite upon us. It is unnecessary to dwell at greater length on this new discovery than will suffice to convince you of its authenticity. The mosquito theory of malaria has been urged by several writers, during apparently the last hundred years -among others, more recently, by Laveran and Koch; and I may add, it is held by some barbarous tribes who have only too great an experience of the disease. But the idea did not obtain scientific form until Dr. Patrick Manson expounded his famous theory, based on certain recondite changes in the parasite, that this organism requires a suctorial insect for its further development. This induction—which I hold to be one of the profoundest and most important inductions in science— not only gave substance;to what was previously littlebut hypo¬ thesis, but showed exactly how the subject was to be attacked by the experimental method. Manson published his views in 1894, and I began the required experiments in 1895. In August’ 1S97, I first succeeded in cultivating the parasites of malaria in two species of mosquito; and by August, 1898, the develop¬ ment of one of the parasites of birds in the mosquito had been worked out, and healthy birds had been infected by the bites of infected insects—thus completing the life-cycle of these organisms. In scientific work, however, before any new observation is accredited it must be confirmed and accepted by men of recognised scientific standing. I should therefore mention that my labours were repeated and confirmed last December by Dr. Daniels of the Malaria Commission, who was sent to me to Calcutta by the Royal Society and the Colonial Office1 • by Professors Grassi, Bignami, and Bastianelli, of Rome2; and later by Dr. Koch®. Valuable details have been added by these observers and by Dr. MacCallum in America; and the whole researches are now accepted by those distinguished men of science: Dr. Manson4, Professor Ray Lankester, Dr. Laveran5, and M. Metchnikoff, and have formed the subject of admirable memoirs by Dr. Nuttall8 and Dr. Mesnil7. All these gentlemen constitute a jury from whose opinion it is impossible to appeal; and the public may therefore safely accept their verdict. Hence, instead of our vague surmises of yesterday regarding malaria we have now a large body of exact observations to depend upon for our facts. We can follow the actual parasites which cause the disease step by step in their development in the mosquito, and we can detect them in that gland of the insect which secretes the irritating poison injected into us