“ The bird-lice (Mallophaga) are far more numerous in species, although the number of genera is comparatively small. With the exception of the genus Trichodectes, the various species of which are found on mammalia, all infest birds (as their English names implies) (see Bird-Louse) . Louse-infestation is known as phthiriasis in medical and veterinary terminology. ”

“ A third human louse, known as the crab-louse (Phthirius pubis) is found amongst the hairs on other parts of the body, particularly those of the pubic region, but probably never on the head. The louse of monkeys is now generally considered as forming a separate genus (Pedicinus) , but the greater part of those infesting domestic and wild quadrupeds are mostly grouped in the large genus Haematopinus, and very rarely is the same species found on different kinds of animals. ”

“ Want of cleanliness favours their multiplication in a high degree—the idea once existed, and is probably still held by the very ignorant, that they are directly engendered from dirt. The irritation is caused by the rostrum of the insect being inserted into the skin, from which the blood is rapidly pumped up. ”