"These are great etiological facts. They are of supreme practical and scientific value. Acting on them, the United States sanitary authorities expelled yellow fever from Havana. Acting on them, they should be able in the future to protect the United States themselves from such terrible visitations as in the past have swept through some of your cities."
3. Filariasis
These same lectures contain an admirable account of the life-history of Filaria. It is not necessary here to describe the loathsome deformities which occur in the later stages of filariasis. These deformities (elephantiasis, Barbadoes leg), which may attain colossal size, are due to the blocking of the lymphatic vessels with filarial worms. Cases of the disease are hardly ever seen in this country; but it is very frequent in some parts of the tropics. In the endemic areas, says Manson, 10 per cent. is not an uncommon proportion of the population to be found affected with filariasis. Thirty and even 50 per cent. may be affected. In many of the Pacific Islands—the Samoa group for instance—I believe that even this proportion is exceeded.
That Culex (fatigans) can carry the parasite, has been proved past all doubt. Neither does anybody doubt, that the keeping down of this mosquito would keep down filariasis. A report of great interest, from Barbadoes, was published in the British Medical Journal for 14th June 1902. It is written by Dr. Low, whose experiment on himself in the Campagna has already been noted in this chapter. Dr. Low reports that there is no indigenous malaria in the island, and that neither he nor Mr. Lefroy could find a single Anopheles larva, though they hunted diligently in the swamps and other likely places. But filariasis is terribly common, and so is Culex fatigans. Dr. Low examined the night-blood of 600 cases of all kinds in the General Hospital, the Central Almshouse, and elsewhere, and found the filaria-embryos in no less than 76 = 12.66 per cent. He caught and dissected a hundred mosquitoes (Culex fatigans) from the wards and corridors of the General Hospital, and found that no less than 23 of them were infected. If it were not for Culex, and for men's indifference and apathy, filariasis could be kept down all over the island:—
"There is a perfect water supply, and people can get their water fresh from the standpipes at their doors. Old wells ought to be filled up; no water-barrels or tubs should be allowed, or, if kept, they should be emptied every week or so. Tanks and collections of water in gardens should all be periodically treated with kerosene, or be furnished with closely-fitting covers to prevent mosquitoes getting in. These methods are simple and inexpensive, and each householder should see that they are applied in his garden and grounds. The difficulty begins when one has to take into account the inability of the negro to grasp anything of a hygienic nature. The only way to get over this, would be a system of sanitary inspection by a few competent men. For individual prophylaxis, mosquito-nets ought always to be used; but many, even educated people, still persist in sleeping without them; of course, nothing in this line can be expected of the native population.
"If such means were adopted for Barbadoes, the presence of filarial disease, which at present is quite alarming, could easily, with little trouble and expense, be greatly diminished, and thus save much suffering, as well as loss of time, hideous deformity, and doubtless in not a few instances loss of life."
Thus, in a few years, from experiments on mosquitoes, sparrows, and men, has come the present plan of campaign against malaria, yellow fever, and filariasis; that is, against Anopheles and Culex. He who would know what is being done to check these diseases in Italy, India, China, Africa, and America, must read Prof. Ross' Malarial Fever, its Cause, Prevention, and Treatment (1902), and Mosquito Brigades, and how to organise them (1902). There has been nothing like it since Pasteur died. Far and wide, from Staten Island to Cuba, from Hong Kong to Lagos, the work of keeping down the larvæ of Anopheles and Culex is going on. Henceforth we have to reckon not with a nameless something, but with a definite parasite, whose conditions of life are known. Before all things, we must shut off the sources of the infection. For centuries, men had believed in exhalations and miasmata lying all over the land: and, behold, the agents of malaria are in the puddles round a man's house, and the agents of yellow fever are in the water-butt and the broken bottles and old sardine-tins. Science has given the word, and now there are Anopheles brigades and Culex brigades set going; labourers with brooms and rubbish-carts, sweeping out the stagnant pools, draining the surface soil, and carrying off the odd receptacles that serve to hold mosquito eggs and larvæ. The job, like all sanitary jobs, must be steady, year in, year out: it must be limited to infected places, a whole continent cannot be treated. But there the work is, and will grow; and saves, by unskilled labour, and at a trivial expense, those "non-acclimatised" lives that have hitherto been thrown away as recklessly as the larvæ that are now swept out of the puddles and ditches round African settlements.
XI
PARASITIC DISEASES
The foregoing chapters are concerned with bacteriology alone, and with those curative or preventive methods of treatment that have come out of inoculation-experiments on animals. The lives that are saved, or safeguarded, by these methods, even in one year, must be many thousands in each country of the civilised world. And, beside human lives, there is the protection of sheep and cattle against anthrax, swine against rouget, horses against tetanus, cattle against rinderpest. In Cape Colony alone, so far back as 1899, about half a million cattle had received preventive treatment against rinderpest; and the sum total of human and animal lives saved or safeguarded, in all parts of the world, must be reckoned in millions by this time.
The present chapter, and the next two chapters, are concerned with methods that have come out of experiments on animals, but not out of bacteriology.