Fig. 47.—Ixodiphagus caucurtei laying eggs in the nymph of Ixodes ricinus. × 20. (After Brumpt.)
Ixodes ricinus, of a brownish colour in the male, is very common in England and, indeed, almost everywhere. The female is yellow and flattened, somewhat resembling a grain of rice. It is the well-known dog-tick, but it attacks oxen, goats, deer, horses, and man. It also attacks the grouse, and is particularly common in some parts of Great Britain. It is impossible to rid certain areas of these troublesome guests. In some cases they produce tumours and introduce bacteria, and in cattle it introduces an organism known as Babesia bovis, which is the cause of haematuria in oxen. Dermacentor venustus transmits Rocky Mountain fever, which is common in certain parts of the States. The fever is accompanied with pains in the joints and in the muscles and an eruption on the surface of the skin, appearing first on the wrists and forehead, and invading in time all parts of the body, followed by a scaling of the skin during a period of convalescence. In Montana the mortality caused by this disease is very high, varying in different years from 33 to 75 per cent. In Idaho the mortality is far less, only about 4 per cent.
Ornithodorus moubata inoculates man with a spirochaete (Spirochaeta duttoni), which is the agent of the African tick-fever or relapsing fever. One of the curiosities about the organisms transmitted by ticks is that they live through the whole cycle of the tick’s life. If they are taken in by the larva they are only transmissible by the following larval stage. If they are taken in by the nymph they are only transmissible when again the nymph stage is met with, and the same is true of the adult. Think what such a protozoon must have seen! The fertilisation of the egg by the spermatozoon, the fusion of their nuclei, the extrusion of the polar-bodies, the breaking up of the egg into segments, the gradual building up of the tissues of the larva, the sudden inrush of the host’s blood when the larva is safely fixed, the moulting, the changes in the nymph, the development of the generative organs, the formation of the eggs! What a text-book of embryology and anatomy it could write if only it had descriptive powers! If I may paraphrase Kipling:—
Think where ’e’s been,
Think what ’e’s seen,
Think of his future,
And Gawd save the Queen!
CHAPTER X
LEECHES