Faichne reared maggots in dejecta infected with typhoid bacilli, and he was able to show that the flies into which these maggots turned contained virulent typhoid germs in their intestines. There is absolutely no doubt that typhoid is largely conveyed by the agency of these insects; and as flies are perfectly controllable, if ‘the people will but have it so,’ it is one of the disgraces of our civilisation that this disease should be so prevalent.
The protective inoculation against enteric is now almost perfect, and its value is shown by quotations from a leaflet issued by the Research Defence Society:—
Sir William Leishman, in a letter published during the present war, August 22, 1914, says: ‘The benefits of inoculation are so well recognised in the regular forces that we find little difficulty, in foreign stations, in securing volunteers for inoculation: for instance, about 93 per cent. of the British garrison of India have been protected by inoculation; and typhoid fever, which used to cost us from 300 to 600 deaths annually, was last year responsible for less than 20 deaths. Inoculation was made compulsory in the American army in 1911, and has practically abolished the disease; in 1913 there were only 3 cases, and no deaths in the entire army of over 90,000 men.’
In Avignon, in the south of France, during the summer of 1912, typhoid fever broke out in the barracks. Of 2053 men, 1366 were protected and 687 were not. The non-protected had 155 cases of typhoid, of whom 21 died; the protected had not one case. In the winter of 1913 the French Senate resolved that the protective treatment should be made compulsory throughout the French army; and, in special circumstances, among the reservists.
Fig. 22.—Chart illustrating the relation of the numerical abundance of house-flies to summer diarrhoea in the city of Manchester in 1904. Prepared from statistics and chart given by Niven. (From Gordon Hewitt.)
Infantile diarrhoea, which so afflicts the crowded, poorer quarters of our cities in the summer, is another disease intimately associated with Musca domestica. But that is hardly a disease likely to trouble the soldiers. The tubercle bacillus is another germ conveyed by flies. House-flies are particularly fond of feeding on saliva; and Hayward, Lord, and Graham-Smith have obtained virulent bacilli from the intestines and dejecta of flies which had been fed on tubes containing tuberculous sputum. These experiments have been amply confirmed by other workers. Anyone who has ever been in Egypt will remember the terrible sight of the flies attacking little children suffering from ophthalmia and it is believed that the wide prevalence of this most pitiful trouble is attributable to the abundance of flies—the flies of Egypt, a plague even in the times of the Pharaohs. Things do not alter much in Egypt, and the Biblical plagues are wont to recur.
Another disease—anthrax, or wool-sorter’s disease—may be conveyed by the same carriers from infected cattle to man, and there is a good deal of epidemiological and bacteriological evidence available to show that flies play an important part in the spread of cholera, which is now threatening the soldiers in the eastern seat of the war, and possibly in disseminating the organisms which cause yaws and tropical sore.
It will be noticed that the fly is not a necessary second host for any of these germs. They are conveyed, as if by an inoculating needle, by contact with the proboscis or the legs or some other tainted organ of the fly. The bacilli, however, pass through the alimentary canal apparently unchanged and unharmed, and are deposited either with the regurgitated food from the fly’s stomach ([Fig. 20]), or with the dejecta of the insect. There is no subcutaneous inoculation—such as takes place in the case of the mosquito when it conveys malaria, or in the case of the tsetse-fly when it conveys sleeping sickness—where the disease-causing organism is injected into the human body. The action of the fly is mechanical, but none the less efficient. The poisoning of the soldiers’ food-supply is its chief rôle in war.