particularly on the hairy parts of the legs, the organisms of infectious disease, the eggs of various parasites, and organic filth. Should they next visit our tables, this dangerous material is distributed over our food. When food so contaminated is taken into the stomach, man is directly infected and may develop any one of a number of diseases.

Another manner in which flies disseminate infection is through the regurgitation or vomiting of food. It is unpleasant to consider that insects which have but recently frequented garbage heaps, cuspidors, and manure piles may be guests at our tables, but it is all the more disgusting to consider that the very material of which they have partaken should be subsequently distributed over our own food and then received into our system. Similarly, the numerous brown excreta spots or fly specks on walls and ceilings which are the bane of every housewife prove by their very location that they should be far less the objects of hatred than those which are deposited elsewhere. The number of such vomited and fecal spots deposited by well-fed house flies may be enormous, frequently rising to a hundred or more a day.

The range of flight of house flies is ordinarily not great. They probably seldom travel more than half a mile from their breeding place unless carried by winds, and usually remain within 200 or 300 yards of their point of origin. Therefore, if flies are found in a particular neighborhood it is fair proof that they developed in the immediate vicinity. The range of flight may be ascertained by anyone who is interested in such experiments by coloring insects with aniline dyes and, following their release, recapturing them either by traps or fly paper at various distances.

Flies are attracted to houses either by the odor or presence of food. Warmth also proves seductive. In cold weather they seek shelter to hibernate, crawling into unexposed places and living for several weeks in a semidormant condition. Following the onset of warmer weather they revive and become the forbears of a numerous progeny, thus continuing the race from season to season. For this reason exterminative measures are of greatest value if begun early. It is also probable that continuance through the winter season is due to the prolongation of the egg and larval stages by the low temperature. In spite of a considerable resistance to cold which flies manifest they are at the same time quite susceptible to its influence, preferring quietude to activity when so affected. Sunlight and brightness are usually attractive, a fact familiar to every housewife.

Carriers of Disease.

Flies may transmit disease in either of two ways. The first method is by mechanical transference, whereby the insect becomes contami

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nated with the parasites or microorganisms of disease as a consequence of frequenting filth and places where these agents abound, thus carrying pathogenic organisms directly to food or drink partaken of by man. This is by far the most common method of conveyance. All forms of flies may act as disease carriers in this manner, but the house fly is the principal offending species owing to its prevalence and great tendency to frequent filth. As previously stated the body of the fly with its stiff, hairy parts is well adapted to transference of contagion in this manner.

Experiments have been conducted to show the length of time flies. may carry the organisms of infection, but this naturally varies. If conditions are favorable, there is little doubt that bacteria may be transferred in this manner after several days. If the organisms are taken into the intestinal tract of the fly, this period may be lengthened, the feces serving as the agent of transmission and prolonging the infective stage. When it is realized that milk, which is one of the best media for the growth of bacteria, may be contaminated by flies merely through the act of feeding and that "clean flies" may even derive infection from those which have but recently visited outhouses and stables, the dangers of food contamination may be conceived.

The second method of disease transmission is by inoculation, that is the actual injection into the system by the insect of pathogenic organisms or parasites. Fortunately, disease can not be transmitted in this manner by the nonbiting flies, else our safety would be far less than at present, the bloodsucking varieties being only those which are of danger in this respect. In our country these varieties are relatively infrequent. The mode of transmission is similar to that in which malaria is conveyed by the mosquito, typhus fever by the louse, and plague by the flea. The parasites or organisms derived from the blood of the infected person are received into the stomach of the fly, where they may undergo developmental changes requiring a specified period, and are subsequently inoculated into a second individual.

Of the diseases which may be transmitted by flies the following are worthy of consideration: Typhoid fever, diarrhea and enteritis, cholera, dysentery, paratyphoid fever, intestinal parasitic infections, sleeping sickness, surra, nagana, with a number of others where there is a distinct possibility of transference.

Typhoid fever is the most common and important infection of man conveyed by flies. It is an acute, infectious disease of bacterial origin, contracted only by taking into the system the bacteria containing discharges of one actually ill of the infection or of some person who serves as a carrier thereof. It may be contracted through sewage-polluted drinking water, infected shellfish, or in

other manner, the only requisite being the presence of the typhoid bacilli in the food or drink of man. It is essentially a disease of filth, but unless means are established for the transference of such filth to the mouths of persons the infection never develops. Flies frequently serve as the means of this transference, and are therefore in part responsible for the dissemination of the disease. In the United States alone during 1914 over 14,000 persons died from typhoid fever and 10 times that number suffered from the infection, the rate being several times higher than that of many civilized

countries.

Attention was called to the agency of flies in the transmission of typhoid fever during the Spanish-American War, when hundreds of our soldiers died from this altogether preventable infection. It was clearly established that the high incidence of the disease was in part due to the presence of myriads of flies which visited the unscreened and unprotected latrines, later to be accorded free access to the kitchens and dining halls of the troops, where every opportunity was available for the contamination of food. In certain instances the very chemicals used in covering discharges were found upon the bodies of the insects and occasionally upon the food itself, indicating that fecal matter was present and that infection in this manner was possible. The investigations of that time have since been confirmed, and it is now a well-recognized fact that whenever flies have access to the discharges of man and at the same time to his food supply disease will necessarily occur.

The conditions which prevailed during the Spanish-American War exist in thousands of American communities to-day. We look with horror upon the frightful and unnecessary sacrifice of lives which then ensued, yet within our very vision identical conditions prevail and we remain quite undisturbed. The unscreened and unprotected privy constitutes a grave and serious menace to the health of any community. Sooner or later it is bound to become the depository of typhoid excretions, and at that moment it becomes a hazard to every resident in the vicinity, for that very environment has created an insect host capable of disseminating the scourge to every point of the compass. It should be understood that typhoid-fever bacilli never originate in flies themselves, but are always derived from infected human dejecta. Not only are the bacilli contained in the feces of man, but in other excretions as well. Persons actually ill of typhoid excrete enormous quantities of such organisms, but these cases may actually be of less danger than others, inasmuch as in the majority of instances proper disinfection and disposal of such material is Secured. Many persons, however, continue to excrete these dangerous organisms long after they are well, in some instances for years, and thus are a constant source of danger to the public. So common is

this condition that at least 2 per cent of those who have recovered from the disease can be rated as typhoid-bacillus carriers. Again, walking or ambulant cases of typhoid are frequent, and in certain instances the condition goes unrecognized or is mistaken for something else, so that necessarily there is, and will continue to be, serious danger through the medium of flies from these apparently harmless persons. In unsewered districts this hazard is proportionately greater, but even in sections properly provided for in this respect the menace is never negligible if flies exist.

Flies which have access to outhouses and to tables may contaminate any variety of food. Milk is frequently subject to infection, and numerous epidemics of typhoid with resulting deaths have been traced directly to dairies unprovided with proper facilities for the disposal of excreta. Given a typhoid carrier and the presence of flies, together with an unprotected privy vault, and the stage is completely set for the development of the drama of disease. Food purchased in fly-ridden markets may likewise be a source of contamination, and if eaten uncooked may lead directly to illness. Cooked food of whatever nature may be contaminated subsequent to the cooking, constituting a serious menace to health. Irrespective, then, of the precautions we exercise as individuals, we are all more or less exposed to the infection of typhoid fever through common sources. Further, as a result of the laxity of others, even when we ourselves may have exercised every precaution necessary to prevent the development of flies, our lives are frequently endangered.

A second infection, and one analogous to typhoid, frequently conveyed by flies, is summer diarrhea. This is more particularly a disease of children, but adults are also susceptible. Annually in the United States 70,000 infants under 2 years of age die from diarrhea and enteritis, the infectious nature of which has now been definitely determined. Bacteria of various varieties are known to be responsible for the disease. The sources of infection are much the same as in typhoid, the causative organisms reaching the alimentary tract as a result of uncleanliness, infected food, and very possibly by contamination of hands or food through the activities of flies. The evidence against the fly as a conveyor of the infection is largely circumstantial, yet so conclusive is it that no one would fail to place the responsibility upon this insect.

First, the disease exists in the summer season, when flies are known to be prevalent. Its incidence varies directly with the incidence of flies, the summer diarrhea curve and the fly curve practically coinciding. This in itself is suggestive. Further, it has been demonstrated that flies are important distributors of bacteria, that they frequent localities where infective organisms are deposited, and that following eradicative measures directed toward these insects there is almost

invariably a decrease in the prevalence of intestinal complaints of this character. It would therefore seem that in the light of our present knowledge we are warranted in the conclusion that flies play a definite rôle in the dissemination of the disease. If we wish, then, to save the lives of the babies the very first step in the process is the eradication of flies.

Cholera and dysentery, which are primarily intestinal affections conveyed in the same manner as typhoid, are unquestionably at times. disseminated by flies. Each is a bacterial disease due to a specific organism, the development of which follows the ingestion of water or food contaminated in some way from the discharges of a person ill with the disease or who excretes the bacilli thereof. It is reasonable to suppose that in a certain percentage of cases flies may act as the distributing agent, and this has been well established with the first-mentioned infection. Fortunately cholera is a rare affliction in this country, originating only from imported cases, but epidemics of dysentery are not uncommon, being especially prevalent in institutions, camps, and districts where insanitary conditions prevail.

In addition to the intestinal diseases cited, certain other affections, more or less closely related thereto, may at times develop as a result of the activities of flies. Paratyphoid, a first cousin of typhoid fever, and food poisoning are to be considered in this category. More important still, however, are the numerous parasitic worms, such as the various species of tapeworm, hookworms, and even those of rarer forms, all of which are continued through the media of ova or eggs contained in the feces of infected persons. Many species of flies are attracted by the ova of such worms and readily devour them, with the possibility of passing through the fly undigested, with later transference to articles of food and thence to the mouths of persons, thus completing the cycle from man to man. It is believed that a certain percentage of cases of infection with intestinal parasites have their origin in this manner. Not only this, but it has been shown that flies developing from larvæ which have fed on parasitic worms may harbor the immature forms of the parasites for several days in the intestinal tract, subsequently to scatter them broadcast.

A most interesting disease in which it is clearly established that flies act as the sole agent of transmission is sleeping sickness, this being an example of conveyance by inoculation. The infection is due to the invasion of the blood and body fluids by a parasite known as a trypanosome, which lives and multiplies after it has once been introduced. Analogous parasites exist in the bodies of mammals other than man. Rats, for example, are frequently found to harbor a species of trypanosome, but curiously no symptoms develop. In