The eggs and larvæ of anopheles are more apt to be found in natural pools and puddles, which do not become dry too quickly, than are those of culex, which are commonly to be detected in such artificial collections of water as pails, tubs, or cisterns that are about the premises. Ano

FIG. 26. Showing, on the left, anopheles in resting position, its dappled wing. and the position of its larvæ in water; on the right, culex in resting position, its plain wing, and the position of its larvæ in water. The arrows indicate the directions taken by the larvæ when the water is disturbed.

pheles apparently prefer to deposit their eggs in puddles containing certain green algæ; at all events, an association. of anopheles larvæ and particular varieties of green waterplants has been noted by a number of observers. The larvæ of culex are much more apt to be found in collections in or near houses than are those of anopheles, which are to be detected, as a rule, in pools, ponds, or puddles more or less distant.

While anopheles may develop at any time between spring and fall, there are grounds for believing that their favorite

breeding time is in late summer and early autumn; at least, some investigators have failed to find them in notoriously. malarious regions earlier than August. This may assist in explaining the late summer and early autumnal preponderance of malaria in certain places. Nothing is known as to the migratory tendencies of mosquitoes; but the fact that anopheles are known to have been conveyed from malarious regions in hay, on clothing, and in railroad trains serves to explain the occasional occurrence of malarial fever in localities usually regarded as free from it. In several instances anopheles have been detected in places free from malaria, being apparently indigenous. They had manifestly never had the opportunity of becoming infected by sucking the blood of malarial subjects.

The manner in which the mosquito acquires the parasite and conveys it to man is briefly as follows: On sucking the blood of a malarial subject the parasite is taken into the stomach and intestines of the insect. It passes thence by a variety of stages to the salivary glands, where it remains. until the mosquito bites again, when, through the muscular effort of sucking blood, the parasite is readily injected into the tissues of the person on whom the insect is feeding.'

Prophylaxis. From the foregoing the prophylactic measures against malarial fevers may be briefly summarized as follows:

Extermination of Mosquitoes.-From what has been said, it is manifestly far more easy to kill these insects and to prevent their development in large numbers by attention to their habitat during their larval stage than by measures directed toward them when in the matured winged state.

1 For an admirable treatise upon the mosquito, in which are given not only the fuller entomological details and habits of the insect, but much of a general character that is both instructive and entertaining, the reader is referred to Notes on the Mosquitoes of the United States, by L. O. Howard, Ph. D., Bulletin No. 25, New Series, United States Department of Agriculture; also, "Studies in Relation to Malaria: The Structure and Biology of Anopheles," by Nuttall and Shipley, Journal of Hygiene, vol. i., No. 1, Jan., 1901; also, "Notes on the Life History of Anopheles Maculipennis (Meigen)," by Sambou, Brit. Med. Jour., Jan. 26, 1901.

With this in view, no vessels of water into which the female can deposit her eggs should be permitted to stand about the place. All pools and puddles of any considerable size should be permanently drained, and all small depressions for the collection and retention of rain-water should be filled in.

The collections of water about the house-as rain-water barrels, cisterns, old cans, pails, etc.-are more apt to harbor culex larvæ than those of anopheles. The latter, as has been said, are to be sought for in more or less permanent pools or in puddles farther afield, and usually in puddles, not necessarily stagnant, that are supporting the growth of green water-plants.

Where circumstances make it impracticable to drain off or fill in depressions in which water collects and remains, the larvæ may be destroyed by sprinkling the surface of the pool with petroleum or some other light oil, in the proportion of about half a teaspoonful to the square yard. The action of the oil, which quickly spreads over the surface, is to prevent the developing larvæ from getting access to air, for it is principally for respiratory purposes that they come to the surface. All pools that can be permanently drained should be treated in this way, and afterward drained.

To prevent being bitten by mosquitoes, the most scrupulous attention should be given to the screening of all doors and windows of the house; and as an additional precaution the beds should be supplied with mosquito-curtains that should be frequently inspected for the presence of the insect and for rents through which the mosquito may gain access. The dwelling should be built as high above the ground as practicable, and as far removed from manifest foci of insect development as convenience will permit.

In malarious districts one should avoid, as much as possible, going about in the open between sunset and sunrise, and should under no circumstances sleep unprotected in the open air of such localities during either day or night.

Since anopheles especially are known to hibernate preferably within and about the eaves of houses, barns, and other

outhouses, and since the hibernating ones are usually impregnated females, periodic search for them should be made in these places as well as in the dwelling, and all the insects found should be destroyed. In this connection, Major G. M. Giles, in his Handbook of Gnats or Mosquitoes, makes the valuable suggestion that during the hibernating season all buildings likely to harbor the impregnated anopheles should be thoroughly renovated, lime-washed, and fumigated with sulphur.

Of equal importance to the foregoing is the destruction of the malarial parasite at the source of supply, viz., in the blood of malarial patients. In the most recent of his reports from German New Guinea, Koch' expresses the opinion that there is no more important prophylactic measure than this; and when we consider that the malarial human being is probably the sole source from which mosquitoes become infected the weight of this opinion is at once manifest. To this end he advocates the vigorous employment of quinine until the blood of the patient is permanently free from the parasites. The experience of his commission in German New Guinea leads him to suggest the following plan for the use of this drug: During the morning hours of the afebrile period a gram of quinine is to be given daily until the parasites disappear from the circulating blood, as determined by the usual method of microscopic examinations of blood from the lobe of the ear or the finger. The drug is then omitted for an interval of seven days, when on each of the two succeeding days a gram of the drug is again administered; there is then another interval of seven days without quinine, followed by two days of drugging as before. This is continued for a month. In the majority of cases this line of treatment has resulted in the permanent disappearance of the parasite. If relapses occur, this system of treatment should be repeated. During a temporary sojourn in malarial regions strangers should fortify themselves against infection by small doses of quinine, three to five grains on rising every morning.

1 See Deutsche med. Woch., April 26 and May 3, 1900; also Brit. Med. Jour., Feb. 10 and May 12, 1900.

YELLOW FEVER.

Definition. An acute, specific, febrile disease of tropical and subtropical climates that is characterized by jaundice, hemorrhages from the mucous membranes, vomiting of dark or black, grumous matters (the so-called “black vomit”) and albuminuria. It occurs endemically in certain districts of the tropics, and at times spreads epidemically over regions beyond the zone of endemicity. Though its cause is not known, it is obviously an infectious disease. It is not regarded as contagious-i. e., directly transmissible from the sick to the well.

Etiology. Notwithstanding the fact that a good deal has been said and written during the past few years on the etiology of this disease, there are still good grounds for believing that the exciting cause of yellow fever has not yet been discovered.

The contributions upon the subject that until recently received the most serious consideration are those of Sternberg and of Sanarelli,

In 1888 Sternberg called attention to the micro-organism, designated by him as "bacillus X," that he had found in about 50 per cent. of fresh yellow-fever cadavers examined by him. He did not certainly regard it as the cause of the disease, though, because of its pathogenic properties and its presence in only yellow fever, he thought it might possibly be, in some way or other, concerned in its etiology.

In 1897 Sanarelli described a bacillus, designated by him as "bacillus icteroides," that he had discovered in 58 per cent. of yellow-fever cadavers examined by him at Monte Video. From its presence in only yellow-fever cadavers, its pathogenesis, and the peculiarity of the lesions produced in animals inoculated with it, he feels justified in regarding it as the specific exciting cause of yellow fever. He claims to have rendered animals immune from the disease by the use of his cultures of this bacillus, and he further states that the serum obtained from such immune animals has the property of protecting individuals into whom it may be injected from