The flea is most abundant in Europe and the North of Africa. Certain circumstances particularly favour its multiplication; being most abundant in dirty houses, in barracks, and in camps; in deserted buildings, in ruins, and in places frequented by people of uncleanly habits. Other kinds of fleas live on animals, as, for example, the cat flea, the dog flea, and those of the pigeon and poultry. We shall say a few words about a peculiar species which abounds in all the hot parts of America, but principally in the Brazils and the neighbouring countries. This formidable species is the Chigo (_Pulex penetrans_). The chigo, called also the tick, is smaller than the common flea. It is flat, brown with a white spot on the back, and is armed with a strong pointed stiff beak, provided with three lancets. It is with this instrument that the female attacks man with the intention of lodging in his skin and bringing forth her young there. The chigo attacks chiefly the feet. It slips in between the flesh and the nails, or gets under the skin of the heel. Notwithstanding the length of the animal's beak, introducing itself beneath the skin does not at first cause any pain; but after a few days one is made aware of its presence by an itching, which, though at first slight, gradually increases, and ends by becoming unbearable. The chigo, when under the skin, betrays itself by a bump outside. Its body has now become as large as a pea; in the attacked skin a large brown bag containing matter is formed. In this bag are collected the eggs, which issue from an orifice in the posterior extremity, and are not hatched in the wound itself, as was long thought to be the case. The chigoes are an object of terror to the Brazilian negroes. These formidable parasites sometimes attack the whole of the foot, which they devour, and thus bring on mortification; many negroes losing the bones of some of their toes by the ravages of these dangerous creatures. To guard against their attacks, they wear thick shoes, and examine their feet carefully every day. The plan usually followed in the Brazils to prevent the chigoes from injuring the feet, is to employ children, who, by their sharpness of sight, can easily perceive the red spot on the skin where the chigo has entered. These children are in the habit of extracting the insect from the wound by means of a needle. But this is not without risk; as, if any portion of the insect remains in the wound, a dangerous inflammation may ensue. For this reason, operators who are renowned for their skill are much sought after, flattered, and rewarded by the poor negroes of the plantations. [Illustration: Fig. 18.--Louse (_Pediculus capitis_) magnified.]