It is a curious fact that the coloured races of men--especially those of Africa--have little or no objection to being bitten by flies. They seem to accept the attention of flies and ticks with indifference. The men sleep in the day under trees, and are willing food-supply to the insects. The eyelids of children are literally inhabited by flies in some countries, and the folds of the skin of fat adults hide whole rows of fast-holding ticks. But the white man does not willingly permit either fly, flea, or gnat to settle on him. He is (or has been), nevertheless, unwisely tolerant of house-flies in his habitations, and the poorer and less cleanly population are in large proportion infested with wingless insects. The newly established knowledge that certain flies (glossina or tsetse-fly) are the carriers of sleeping sickness, that gnats are the carriers of malaria and of yellow fever, that fleas are the carriers of the plague, and that certain kinds of ticks are the carriers of cattle-fevers and dog-fevers, and probably of some obscure fevers of man, must make us all more anxious than we were about contact with insect life. For ages popular tradition has ascribed diseases of one kind and another in various parts of the world to the bites of flies. But actually it is little more than fifty years ago since it was really shown that deadly germs or parasites existed which could be, and actually are, carried by flies from one animal to another, and introduced into the blood by the flies’ stab. This was first shown in regard to the bacterium of splenic fever (or anthrax, or wool-sorters’ disease), a blood-disease of cattle which is transferred by the big, fiercely-biting “horse-flies” (tabanus), from animals to man, and is invariably fatal. Another bacterial disease, “pernicious œdema,” is inflicted on man in the same way. These cases were exceptional, and it is only quite recently that the agency of flies and fleas in great epidemics, and in diseases causing thousands of deaths every year in well-known regions, has been discovered.
The wingless parasites known as pediculi are not known as active agents in spreading disease germs, probably because they do not readily transfer themselves from one animal to another. It is in this connection a really remarkable fact that monkeys are not infested by fleas, and that only in few cases and not in many kinds have pediculi or acari been observed. In this respect the lower races of men (and even the higher) seem to have fallen away from a grade of excellence attained by their despised quadrumanous cousins. When this fact as to the freedom of monkeys from insect parasites is mentioned, those who have watched monkeys in captivity will immediately say, “Surely I have seen monkeys carefully picking insects from one another’s fur.” The fact is that it is this very habit of “picking” which prevents monkeys from harbouring fleas. Whereas a dog or a cat can only scratch, the monkey has an opposible thumb and delicately sensitive fingers. That which has become the hand of man, with all its marvellous skill and efficiency, has been elaborated in its early stages as a means for keeping the hair clean. When monkeys are seen carefully removing something with finger and thumb from their own or their companion’s hair, it is not an insect but a little piece of fatty secretion and scurf which is thus removed. The habit, which seems to be general in all kinds of monkeys, even with the anthropoids, such as the chimpanzee and the orang, has of course been efficient in removing any parasitic insects which may at one time have infested monkeys--all other furry animals are liberally supplied with them, as also are birds--but is now preventive of any re-establishment of such visitors. The popular judgment of the monkey’s habit is similar to that of the Japanese Aino, who remarked to a traveller who arranged to have a bath in his room every day that he must be a very dirty man to require it.