owing to the obvious difficulty of locating the cases.

The disease

is not one which strikes terror into a community as does yellow fever, many patients failing even to call a physician. In yellow fever, isolation of cases has been long practiced, but has been found insufficient to free any large group of people from the presence of yellow fever if once established.

The screening of houses, while perhaps affording a measure of protection to a community, is likewise only an adjunct, because the mosquito vector bites by day as well as night and it is not possible for any large number of people to remain continually indoors. Screens used against ægypti must be at least 16 mesh, if the wire is heavy, or 18 mesh per inch if the strands are of smaller diameter. Care must also be taken that ægypti does not breed inside the screened inclosure.

Mosquito control. This is the one method to be relied upon in controlling dengue; and as communities where Aëdes ægypti are present are subject not only to dengue but to the spread of yellow fever as well, there are more than ample public health reasons for controlling the pests.

The part (if any) which mosquitoes other than ægypti play in the spread of dengue fever must await further study. However, dengueous regions are usually also badly infested with malaria, which constitutes an urgent necessity for including anopheles among the species of mosquitoes to be attacked; and measures against these two varieties will largely control Culex quinquefasciatus and other mosquitoes which constitute at least an annoying pest irrespective of any influence which they may exert in dengue. Moreover, such a combined attack upon Anopheles and Aëdes ægypti is far more likely to receive the continued financial support of a community than is an attack against either one, since it will more nearly free the community of the mosquito pest. Again, an adequate supply of piped water, so highly desirable for other reasons, is also an important factor in the reduction of available breeding places for mosquitoes. In connection with this article the control of Aëdes ægypti only will be discussed, as it is probably the most important, if, in fact, not the only vector of dengue in this country.

To be successful, mosquito control should be begun before dengue makes its appearance in the community, as control measures are largely directed against wrigglers, and the imagoes in flight will suffice to spread the disease, once introduced, before the control measures can effect the eradication.

Carter, at Paita, March 3, 1920, by systematic work, had the agypti breeding index so reduced that he knew yellow fever cases Unpublished lecture at Hygienic Laboratory.

would cease. The last case appeared 52 days later, produced, of course, by the adults in flight. It would therefore appear that the life of the adult female in flight is in the neighborhood of this period (52 days). Measures against the winged insect, such as fumigation, have been tried, but are time-consuming, difficult, and too expensive for practical application.

Control of Aedes ægypti.-In practice the measures at one's disposal may be enumerated as follows:

1. Destruction of containers.

2. Covering of containers.

3. Placing of fish in containers.

4. Periodic emptying of containers.

5. Oiling of containers.

6. Education and law enforcement as valuable adjuncts.

1. Destruction of containers.-Destruction of containers which serve as breeding places is naturally the best method to pursue. The procedure, however, presupposes a corps of intelligent men working under trained inspectors who will zone the city and instruct and direct the men under them. Men for this work must be intelligent, tactful, acquainted with the habits of the mosquito, and possessed of infinite patience as well as courage. Men should be supplied with notebooks, ladders, screening or muslin, oil, buckets of minnows, etc. It may be found more advantageous to have separate gangs, to correct the faulty conditions found by the inspectors.

Premises must be inspected from the housetop to the cellar, including wells, cisterns, etc. Trash, cans, and other refuse, after being collected, should be dumped into salt water or buried, since hauling to a dump will simply transfer the breeding to other places.

Grass and weeds should be kept cut from vacant lots, since this growth constitutes an inviting place for the throwing of rubbish and a place where, once deposited, it is difficult for the inspectors to locate it.

In the Philippines the rain spouting of houses was found to be one of the chief sources of mosquito breeding and one of the most difficult to remove. When there is a little sag or pocket of water ægypti will breed in numbers, and, if rain follows, the eggs or wrigglers will be washed into the rain barrel or cistern, where they can continue their development. The punching of small holes in spouting has been tried but is useless, as the holes soon become plugged, and larger holes render the spouting valueless. Its complete removal would be preferable. If this is not possible, it should be given a steep pitch to insure drainage. The axils of leaves in such plants as the banana tree and spider lily, while probably not a large factor in the breeding of ægypti, are difficult to deal with. McCoy evolved

the scheme of placing sawdust in this water for the purpose of hastening evaporation.

2. Covering of containers.-This procedure is applicable to wells, cisterns, rain barrels, and similar water containers. A piece of muslin tied over the top of a barrel or cistern is just as efficacious, is cheaper, and is much easier to apply than is the proper fitting of a rigid screen cover. Water barrels should be provided with spigots, and cisterns with pumps, so that water may be drawn without removing the cover, for to do so may liberate a swarm of adults which have developed there from eggs washed in from the eave spouting.

3. Placing of fish in containers.-Minnows are a great help in the eradication of ægypti. Connor and Hanson used them extensively at Guayaquil and Peru in rain barrels, cisterns, wells, and other water containers. Not only do they devour the larvæ, but they facilitate the work of inspection, for it is easier and simpler to see if the fish are living than it is to search for wrigglers.

4. Periodic emptying of containers.-Containers not otherwise protected should be emptied once each weel: (at least every nine days). To empty oftener is a waste of energy. In emptying it is important that every bit of water be turned out, for when wrigglers are disturbed they go to the bottom of the containers, and the last water remaining will contain most of them. It is a good plan to wipe the container with a cloth, which will insure complete emptying and also the destruction of any larvæ or eggs left clinging to the vessel.

After the more accessible breeding places have been destroyed, screened, or oiled, the female mosquito will employ great ingenuity in searching out a place to lay her eggs. Thus she may be driven to use places which are relatively inaccessible or difficult to locate and control. To meet this contingency the trap breeding place has been devised. This consists of placing an inviting container of water in a suitable place-best one fairly dark--and then emptying it once a week.

5. Oiling of containers.-A thick film of oil upon the surface of rain barrels, cisterns, etc., will effectively prevent mosquito breeding. It was formerly supposed that the larvae were killed by suffocation, but it has been found that if larvæ are kept confined so that they can not reach the surface they can live for hours and that the film of oil actually kills in some other way, possibly by poisoning.

6. Education and law enforcement.-The education of the community should be a definite part of any antimosquito campaign, for, if the cooperation of the citizens can be secured, much quicker and more permanent results will be attained.

With the exception of granting legal access of the authorized inspectors to premises, laws have little place in a mosquito campaign

and will always fail to accomplish desired results. The work is technical, requiring the systematic attention of trained men, and is properly a function of the health department.

By the proper application of the above methods it is possible to rid a community of most of its Aëdes ægypti; it is extremely difficult to get rid of them all. Luckily, however, it is not necessary or indeed desirable (on account of the expense) to try to rid a community of every mosquito. All that is necessary to render a community safe from a dengue epidemic is to keep the mosquito index at a point at which introduced cases will not spread, or, let us say, at which 10 introduced cases will give rise to 9, 8, 7, or less number of cases, when, evidently, the disease will soon die out. The exact degree of eradication at which this will occur is not easy to define definitely, but it is some considerable degree short of total extinction.

Animal Transmission.

Occurrences have been recorded (Sandwith, Hirsch) for India, Cadiz, Algiers, and Senegal, in which dogs, cats, sheep, cattle, rats, mice, and birds have suffered epizootics coincident with the presence of dengue among the human population.

Kraus attempted to produce the disease in guinea pigs by the injection of blood from patients. The guinea pigs were observed for eight days, but neither fever nor other symptoms appeared during this time.

Cleland et al. likewise tried to produce the disease in guinea pigs and rabbits, but also with negative results. One guinea pig, injected with blood which produced the disease in a volunteer, was killed at the end of seven and one-half days, and its blood injected into a second volunteer. No symptoms followed. This would indicate that the virus was not present in the guinea pig's blood at this time. The tissues of animals killed at various times following inoculation were examined by various methods of staining, including Levaditi's method, but no abnormalities or spirochetes were found.

Lavinder and Francis tried to infect rhesus monkeys with blood drawn during the second to fifth day of the disease. No symptoms, fever, or skin eruption resulted during 14 days of observation in any of 9 monkeys. The investigators considered their attempts to have resulted negatively; however, they thought that the blood counts were perhaps suggestive enough to warrant further trials.

Chandler and Rice, 1922, attempting to convey the disease to guinea pigs, white mice, and a young rhesus monkey secured only negative results. Their attempts to culture an organism from the blood were likewise unsuccessful.

The writer, 1922, attempted to convey the disease to guinea pigs, rabbits, white rats, and rhesus monkeys, but with negative results.

Animals were injected with blood taken at various stages of the disease (fifth hour to convalescence). The animals were observed for from 8 to 30 days in various cases. In no instances was the behavior of the injected animals different from that of the controls. Blood counts were made in monkeys, rabbits, and rats, but no variations deemed significant were noted. In the case of the guinea pigs, however, the results were complicated by an epidemic of broncho-pneumonia which broke out among them after about the fifteenth day. Controls and injected animals were alike attacked. These experiments will be made the subject of a more detailed report. The tissues have not yet been examined.

Koizumi et al. used dogs, white mice, rabbits, long-tailed Formosa monkeys, and guinea pigs, but symptoms followed only in the latter. They produced similar symptoms in second guinea pigs by subinoculation, but were unable to secure passage beyond the second series of animals. (In view of these findings it may be mentioned that Cleland carried the virus through four successive transfers in human volunteers.) Their pigs inoculated from human cases usually died in from 7 to 36 days, while blood from these to others caused death in from 5 to 19 days if given subcutaneously or intraperitoneally. However, death is said to have been delayed to from 28 to 34 days if given intravenously.

Holt, using guinea pigs and rabbits, was unable to produce symptoms in them by the injection of the blood of dengue cases, but describes polymorphous organisms seen in the fresh and stained blood of several of these animals.

These discordant results are difficult to explain and it is to be hoped that, wherever dengue may occur, workers will embrace the opportunities of repeating these trials at animal transmission as well as attempt to clear up other of the many points which require further elucidation.

Bibliography.

Adrien, C. (1918): Dengue méditerranéenne observée à l'île Fouad (Syrie). Arch. de méd. et pharm. nav., Paris, vol. 105, pp. 275-307.

Agramonte, A. (1906): Some clinical notes upon a recent epidemic of dengue fever. New York Med. J., vol. 84, pp. 231-233.

Allan, J. C. D. (1909): Dengue, or "three-day fever." J. Trop. Med., London, vol. 12, pp. 301-302.

Allen, A. H. (1908): Notes on dengue in Cuba. New York. Med. J., vol. 87, pp. 358

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Archibald, R. G. (1917): Seven-day fever in the Anglo-Egyptian Sudan. J. Trop. Med., London, vol. 20, pp. 133-135.

Armand-Delille (1916): Note sur les principaux caractères de la dengue méditerranéenne, observés aux Dardanelles et en Macédoine. Bull. et mém. Soc. méd. d. hóp. de Par., 3. s., vol. 40, pp. 1709-1714.