" strikes." In the interval between the bite of an infected
Stegomyia and the appearance of the disease (5 or 6 days) the
blood of the patient contains a virus which, when taken into the
mosquito, may develop into the infective material; moreover,
this virus persists alive and active for three days after the
disease is fully developed, but at the end of this time it disappears,
so far, at any rate, as its infective power is concerned,
from the blood, secretions and tissues of the patient. Further,
there is no evidence that the infective virus is ever transmitted
directly from the patient in secretions or in fact in anything
but blood or blood-serum. The infective material, then, is present
in the human subject for about eight days, during which the
blood and even the blood-serum may serve as a vehicle for
the infective agent. If during this period the patient is bitten
by the Stegomyia the mosquito cannot distribute the infection for
twelve days, but after this the power of transmitting reinfection
persists for weeks and even months during cold weather when
the insect is torpid. As soon, however, as the warm weather
comes round and the mosquito becomes active and again begins
to bite there is evidence that it still maintains its power of
transmitting infection; indeed Boyce states that mosquito's
infected in one year are capable of transmitting infection and
starting a fresh epidemic in the following warm season. When
it is remembered that a mosquito by a single bite is capable of
setting up an attack of the disease, we see how important is
this question.
The Stegomyia, known as the domestic or house mosqmto, is spoken of as the " Tiger " mosquito, " Scots' Grey, " or " Black and White Mosquito, " from the fact that there is " a lyre shaped pattern in white on the back of the thorax, transverse white bands on the abdomen, and white spots on the sides of the thorax; while the legs have white bands with the last hind tarsal joint also white " (Boyce). It is also spoken of as the " cistern mosquito, " as it breeds in the cisterns, barrels, water butts, &c., containing the only water-supply of many houses. It may pass through its various stages of development in any small vessels, but the larvae are not usually found in natural collections of water, such as gutters, pools or wells, if the ovipositing insect can gain access to cleaner and purer water.
The egg of the Stegomyia deposited on the water develops in from 10 to 20 hours into the larval form, the so-called " wiggle waggle." It remains in this stage for from i to 8 days, then becomes a pupa, and within 48 hours becomes a fully developed mosquito. The larvae can only develop if they are left in water, though a very small amount of water will serve to keep them alive. The eggs on the other hand are very resistant, and even when removed from water may continue viable for as long a period as three months. The Stegomyia affects clean water-butts and cisterns by preference. Consequently its presence is not confined to unhygienic districts; they may, however, " seek refuge for breeding purposes in the shallow street drains and wells in the town." The Stegomyia does not announce its advent and attack by a " ping " such as that made by the Anopheles, it works perfectly noiselessly and almost ceaselessly (from 3 p.m. to early morning) so that any human beings in its neighbourhood are not safe from its attacks either afternoon or night.
The most important prophylactic measures against the Stegomyia are ample mosquito nets " with a gauge of eighteen meshes to the inch " (Boyce), so arranged that the person sleeping may not come near the net; these nets should be used not only at night but at the afternoon siesta. Then the living room should be screened against the entrance of these pests, thorough ventilation should be secured; and all pools and stagnant waters, especially in the neighbourhood of houses, should be drained, water-butts and cisterns should be screened and all stagnant waters oiled with kerosene or petroleum, where drainage is impossible. What has been done through the carrying out of these and similar measures may be gathered from the record of the Panama Canal. In 1884 the French Panama Canal Company, employing from 15,000 to 18,000 men, lost by death
60 per 1000 annually (in 1885 over 70 per 1000). In iqo4, when the Americans had taken over the work of construction. Col. W. C. Gorgas undertook to clear the country of the Stegomyia, and within two or three years yellow fever had been eradicated. The death-rate from malaria was also greatly diminished, and by the end of 1907 the death-rate per annum amongst 45,000 workers was only 18 per 1000, a lower death-rate than is met with in many large English towns. Similar examples might be cited from other places, but the above is sufficiently striking to carry conviction that the methods employed in carrying on the warfare against tropical diseases have been attended with unexampled success. These diseases, at one time so greatly feared, are now so much under control that some one has said " ere long we shall be sending our patients to the tropics in search of a health resort." .,
Weil's disease, a disease which may be considered along with> acute yellow atrophy and yellow fever, is one in which there is an acute febrile condition, associated with jaundice, inflammation of the kidney and enlargement of the spleen. It appears to be a toxic condition of a less acute character, however, than the other two, in which the functions and structure of the liver and kidney are specially interfered with. There is a marked affection of the gastrointestinal system, and the nervous system is also in some cases profoundly involved. Hæmorrhage into the mucous and serous membranes is a marked feature. The liver cells and kidney epithelium undergo fatty changes, though in the earlier stages there is a cloudy swelling, probably also toxic in origin. Organisms of the Proteus group, which appear to have the power, in certain circumstances, of forming toxic substances in larger quantities than can be readily destroyed by the liver, and which then make their appearance in the kidney and spleen, are supposed to be the cause of this condition.
Diphtheria. — In regard to no disease has medical opinion undergone greater modification than it has in respect of diphtheria. Accurately applied, bacteriology has here gained one of its greatest triumphs. Not only have the aetiology and diagnosis of this disease been made clear, but knowledge acquired in connexion with the production of the disease has been apphed to a most successful method of treatment. In 1875 Klebs described a small bacillus with rounded ends, and with, here and there, small clear unstained spaces in its substance. He, however, also described streptococci as present in certain cases of diphtheria, and concluded that there must be two kinds of diphtheria, one associated with each of these organisms. In 1883 he again took up the question; and in the following year Loeffler gave a systematic description of what is now known as the Klebs-Loeffler bacillus, which was afterwards proved by Roux and Yersin and many other observers to be the causa causans of diphtheria. This bacillus is a slightly-curved rod with rounded, pointed, or club-shaped end or ends (see Plate II. fig 9). It is usually from 1-2 to 5/i or more in length and from 0-3 to 0-5/1 in breadth; rarely it may be considerably larger in both dimensions. It is non-motile, and may exhibit great variety of form, according to the age of the culture and the nature of the medium upon which it is growing. It is stained by Gram's method if the decolorizing process be not too prolonged, and also by Loeffler's methylene-blue method. Except in the very young forms, it is readily recognizable by a series of transverse alternate stained and unstained bands. The bacillus may be wedge-shaped, spindle-shaped, comma-shaped or ovoid. In the shorter forms the polar staining is usually well marked; in the longer bacilli, the transverse striation. Very characteristic club-shaped forms or branching filaments are met with in old cultures, or where there is a superabundance of nutritive material. In what may be called the handle of the club the banded appearance is specially well marked. These specific bacilli are found in large numbers on the surface of the diphtheritic membrane (Plate II. fig. 10), and may easily be detached for bacteriological examination. In certain cases they may be found by direct microscopic examination, especially when they are stained by Gram's method, but it is far more easy to demonstrate their presence by the culture method. On Loefiler's special rpedium the bacilli flourish so weU at body-temperature about 37° C. — that, like the cholera bacillus, they outgrow the other organisms present, and may be obtained in comparatively
