INSECTS AND DISEASE tuberculosis infection does in man. At certain times and under certain conditions, the disease becomes more virulent, the rats die in great numbers, and infection spreads to human beings. The agent of transmission of the germ from rat to man and from man to man remained to be solved; and in 1897 and succeeding years evidence accumulated by a number of French, English, and Russian investigators began to point more and more strongly toward the flea Fig. 29. HABITAT GROUP OF CALIFORNIA GROUND SQUIRRELS ( Cttellus varitegatus beecheyt) American Museum of Natural History as the intermediate carrier of the germ. Finally the experiments of the Indian Plague Commission rendered this practically certain, for they showed that infection did not spread from a sick to a well rat even when in intimate contact if fleas were absent, while if they were present, the exposed animals quickly came down with the disease. In man it is now known that plague may at times (as in Manchuria) develop a peculiar ‘“‘pneumonic’’ type in which the 53
ba EPID A OO eee germs are discharged from the mouth and nose as in the case of a common cold. Pneumonic plague, therefore, spreads directly from man to man by contact, but in the ordinary or ““bubonic”’ plague the éerms are not discharged in any of the excretions of the body and can only be transmitted by the flea. In northern Asia the rodent host of the plague bacillus is the Siberian marmot or tarbagan, Arctomys bobac, and the first human victims in Manchuria were trappers and dealers in marmot skins. In California, the ground squirrel, Citellus variegatus beecheyi, is infected, and the United States Public Health Service up to September, 1913, had isolated plague bacilli from 1891 different individuals. A number of human Fig. 30. SHIP EQUIPPED WITH GUARDS ON THE HAWSERS TO PREVENT LANDING OF INFECTED RATS cases in California were traced to infection from these animals. The most important carriers of plague germs, however, are the various rats, the black rat (us rattus), the common rat of the middle ages in Europe, the brown rat (V/. norvegicus), which has now generally supplanted the smaller and less ferocious black rat, and the roof rat (M. alexandrinus) which has established itself at many seaports. The modern campaign against plague depends mainly upon the control of the rodent host. Human cases must of course be isolated but the great essential is that possibly infected rats on incoming ships should be excluded from the wharves by rat-Suards on the hawsers, and rats on board destroyed by fumigation. In seaports, or other 54 i eae ‘, ee)
INSECTS AND DISEASE cities where plague infection is likely to enter, comprehensive campaigns must be organized for the removal of breeding and harborage places of rats by cleaning up rubbish, for the starving out of rats by covering garbage and eliminating other accumulations of food, for trapping and shooting and poisoning rats, and for excluding rats from buildings by various forms of ratproof construction. The natural enemies of the rat,—cats, dogs, and ferrets, skunks, foxes, coyotes, weasels, minks, hawks, owls, snakes, and _ alligators—are often of great assistance in this campaign.
Fig. 31. THE SECOND PANDEMIC OF PLAGUE.
EXTENSION OF THE DISEASE BETWEEN 1200 AND 1450 A. D. These methods of rat suppression have been widely successful in their application to the control of bubonic plague. The early history of the present pandemic of plague is precisely like that of the one which began in the eleventh century. It started in China, spread to Manchuria in one direction, and killed its six millions in India. Thence, following the trade routes as of old, plague infection has been carried to seaports all over the world. It has “oO
AMERICAN MUSEUM GUIDE LEAFLETS passed east to Melbourne, Brisbane, and other Australian cities, north to Portugal and Scotland, and around the world to Brazil, Porto Rico, California, and New Orleans. We are actually to-day in the midst of a potential world pandemic of plague like that of the Middle Ages; but our knowledge of the relation of the rat to this disease has made it easy to prevent general spread in any of the countries into which infection has been introduced outside of Asia. Fig. 32. THE THIRD PANDEMIC OF PLAGUE. EXTENSION OF THE DISEASE BETWEEN 1897-1917. 56 RA eb de Aan hh
INSECTS AND DISEASE Fig. 33. MODEL OF THE BODY LOUSE (Pediculus vestimentt) American Museum of Natural History LICE AND BED-BUGS Another group of insects, of great importance in connection with disease, is the family of Siphinculata known as sucking lice or Pediculide. They are small, more or less flattened, wingless parasites which have an unjointed, fleshy beak barely reaching the thorax. The five-jointed antenne are short; the tarsi are singlejointed, forming a claw at the end of the tibiw; the eyes are well developed, convex, and distinctly pigmented. The eggs, “‘nits,’’ are fastened on the hair or clothing of their host. The metamorphosis is slight so that the newly hatched young closely resemble the adults, and there is no resting, pupal stage. Three or four weeks is usually sufficient time for these creatures to reach maturity from the time the egg is laid. The head-louse, Pediculus capitis, is more common 57
AMERICAN MUSEUM GUIDE LEAFLETS on the children of cleanly families than is generally admitted and it is almost the rule among the less cleanly, The former get it from the latter by contact, by using the same comb or brush, by hanging the hat on the same rack in school and in other ways. The bodylouse or gray-back, Pediculus vestimenti (or corporis) is common where men gather in numbers without having, or using, adequate facilities for cleanliness. Cleanliness, in this case, refers very largely to the clothing, as this species lays its eggs on the clothes next to the skin and the lice themselves spend much of the time there. The crab-louse, Phthirius inguinalis, is an easily recognized species, the common name being appropriate. It infests the pubic regions and the armpits of man. Transmission sometimes occurs by way of public toilets.
The use of a fine-toothed comb dipped in kerosene is an effective remedy for the head-louse. The treatment should be repeated twice at intervals of a week. For body-lice, the clothing should be boiled, steamed, fumigated, or soaked in gasolene or benzine. The irritation caused by the lice may be relieved by a lotion of one half ounce of borax to a pint of water. In dealing with these lice when there is danger of typhus fever, the greatest care must be exercised to prevent their spread. The face and the head should be shaved and the hair burned. A liberal use of kerosene on floors and about beds is recommended, The crab-louse may be treated in the same way as the head-louse but mercurial or “‘blue’’ ointment is often used. The salve should not be strongly rubbed in or used directly after a warm bath. Vinegar makes the eggs of the lice more susceptible to treatment.
The Bed-bug, Cimex Jectularius, an insect belonging to the Hemiptera, has received many more or less descriptive names in addition to that of ‘““bed-bug.”’ Some of them are “‘wall-louse,”’ ‘“‘red-coat,”’ “mahogany flat,’ “‘chinch,’’ and just “bug.” Most people are familiar with this insect, whether they admit it or not; others usually recognize it, by instinct or by its reputation, the first time they meet it. There is a mistaken idea that the flat, darkcolored insects to be found under the bark of decaying logs, and the ones that occur in the nests of swallows, belong to the species under discussion. Another mistaken notion is that these creatures may become “‘grandfathers in a night.”’ The eggs, which are white and oval in outline with a rim around the free end and sculpturing over 58 .
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INSECTS AND DISEASE the shell, are laid in cracks and crevices in beds and in bedrooms. These eggs hatch in about a week. The young resemble the adults, except in size, and there is no pupal stage. After molting five times, the adult stage is reached; this growth takes a month or more, depending on temperature conditions and the amount of available food—the blood of man, and, if necessary, of other warm-blooded animals such as mice and poultry. Bed-bugs have been kept alive and active for a year in a tight box without any food at all. Kerosene, gasolene and benzine are effective remedies, if forced into the crevices where the bugs hide by day. The treatment should be repeated at intervals of about a week, since the eggs often withstand this treatment. For killing them on a large scale, there is nothing better than fumigation with hydrocyanic acid gas, but this is a deadly poison for man as well and should be used with caution. Those desirous of trying it should write to their State Entomologist or to the Bureau of Entomology, United States Department of Agriculture, for detailed instructions.
The bed-bug has a few natural enemies; these enemies are, however, not greatly to be preferred to the bed-bug itself. “‘Kissing bug,’ of much newspaper fame a few years ago, is a name applied to several insects which prey upon the better known pest. The “‘masked bed-bug hunter,’ Reduvius personatus, is one of these. The “big bed-bug’’ of the South, 7riantoma (—Conorhinus) sanguisuga, is much more given to sucking human blood. “‘It is about an inch long; black, marked with red on the sides of the prothorax, at the base and apex of the front wings, and at the sides of the abdomen; the head is long, narrow, cylindrical, and thickest behind the eyes. It is said that the effects of its bite may last for nearly a year, and it is probable that attacks which are attributed to spiders are really the work of this insect. Out-of-doors, it feeds on insects, including grasshoppers and potato beetles’ (Lutz, ‘““Field Book of Insects’).
Bebe! See ie ie Sis ote eee LS TYPHUS FEVER AND OTHER DISEASES CARRIED BY THE LOUSE Typhus fever, known also as ship fever, camp fever, and jail fever, was one of the deadliest of the diseases of the Middle Ages. Wherever men were crowded together under the filthy conditions which surrounded our ancestors, this pestilence raged. In sinister alliance with famine, it scourged unhappy Ireland so persistently that it was known as “‘Irish ague.”’ In England its contagion was spread even through the law-courts, and several notable outbreaks among judges, lawyers, and spectators were dubbed the “Black Assizes”’ during the sixteenth century. In Tuscany, between 1550 and 1554, more than a million people are said to have died of typhus. Professor Curschmann says of this malady, ““‘between 1846 and 1848 more than a million cases of typhus occurred in England and more than 300,000 in Ireland, the outbreak starting after the great famine ofthe earlier year. In every century typhus fever has followed in the wake of armies. During the Thirty Years’ War it claimed more victims than did the weapons of the contestants. It was the terror of the Napoleonic campaigns and decimated the French Army, already demoralized physically and morally by the terrible retreat from Moscow. During the Crimean War it decimated both the French and English armies, especially the former.’’ Dr. R. Bruce Low describes the experience of France with “camp fever’ as follows: ‘““When.the French in 1812 began their historical retreat from Moscow, they had at least a thousand fever cases among them, and by the time they reached Vilna many other attacks had occurred with numerous deaths. At the beginning of December, 1812, the Russians had taken 30,000 French prisoners, many of whom were ill of fever. The hospitals at Vilna were overflowing with the sick, who suffered greatly from cold and lack of food. Many had no bed or bedding, and had to lie on rotten straw, sometimes side by side with the dead. Of 25,000 cases sent to hospitals at Vilna, less than 3,000 were alive at the end of January, 1813. From the troops the disease in many instances spread to the civil population. For example, in the fortified town of Metz no fewer than 7,752 soldiers of the garrison died of typhus during 1814, as well as 1,294 other persons in the civil hospitals. From Metz the infection spread to the neighboring districts, and by the end of the year no fewer than 10,329 deaths from typhus had occurred in the 60 i