Basile (1910 and 1911) however, carried on numerous experiments indicating that the disease was transferred from children to dogs and from dog to dog by the dog flea, and was able to find in the tissues of the insects forms perfectly identical with those found in children and in dogs suffering from leishmaniasis. He also found that _Pulex irritans_ was capable of acting as the carrier. Of the cutaneous type of leishmaniasis, the best known is the so-called "Oriental sore," an ulcerative disease of the skin which is epidemic in many tropical and subtropical regions. The causative organism is _Leishmania tropica_, which occurs in the diseased tissues as bodies very similar to those found in the spleen in cases of Kala-azar. The disease is readily inoculable and there is no doubt that it may be transferred from the open sores to abraded surfaces of a healthy individual by house-flies. It is also believed by a number of investigators that it may be transferred and directly inoculated by various blood-sucking insects. TICKS AND DISEASES OF MAN AND ANIMALS We have seen that the way to the discoveries of the relations of arthropods to disease was pointed out by the work of Leuckart and Melnikoff on the life cycle of _Dipylidium_, and of Fedtschenko and Manson on that of _Filaria_. They dealt with grosser forms, belonging to well-recognized parasitic groups. This was long before the rôle of any insect as a carrier of pathogenic micro-organisms had been established, and before the Protozoa were generally regarded as of importance in the causation of disease. The next important step was taken in 1889 when Smith and Kilbourne conclusively showed that the so-called Texas fever of cattle, in the United States, is due to an intracorpuscular blood parasite transmitted exclusively by a tick. This discovery, antedating by eight years the work on the relation of the mosquito to malaria, had a very great influence on subsequent studies along these lines. While much of the recent work has dealt with the true insects, or hexapods, it is now known that several of the most serious diseases of animals, and at least two important diseases of man are tick borne. These belong to the types known collectively as _babesioses_ (or "_piroplasmoses_"), and _spirochætoses_. The term _babesiosis_ is applied to a disease of man or animals which is caused by minute protozoan parasites of the genus _Babesia_, living in the red blood corpuscles. These parasites have usually been given the generic name _Piroplasma_ and hence the type of disease which they cause is often referred to as "_piroplasmosis_." The best known illustration is the disease known in this country as Texas fever of cattle.