In these earlier experiments it was believed that the cattle tick acted as a carrier of the disease between the Southern cattle and the soil of the Northern pastures. "It was believed that the tick obtained the parasite from the blood of its host and in its dissolution on the pasture a certain resistant spore form was set free which produced the disease when taken in with the food." The feeding of one animal for some time with grass from the most abundantly infected field, without any appearance of the disease, made this hypothesis untenable.
In the experimental work in 1890 the astonishing fact was brought out that the disease was conveyed neither by infected ticks disintegrating nor by their directly transferring the parasite, but that it was conveyed by the young hatched from eggs of infected ticks. In other words, the disease was hereditarily transferred to ticks of the second generation and they alone were capable of conveying it.
Thus was explained the fact that Texas fever did not appear immediately along the route of Southern cattle being driven to Northern markets but that after a certain definite period it manifested itself. It was conveyed by the progeny of ticks which had dropped from the Southern cattle and deposited their eggs on the ground.
These results have been fully confirmed by workers in different parts of the world,—notably by Koch, in Africa, and by Pound, in Australia.
The disease is apparently transmitted by Boophilus annulatus alone, in the United States, but it, or an almost identical disease, is conveyed by Ixodes hexagonus in Norway, Ixodes ricinus in Finland and France and by the three species, Boophilus decoloratus, Hyalomma ægypticum (fig. [140] and [141]), and Hæmaphysalis punctata in Africa.
In spite of the detailed study which it has received, the life cycle of Babesia bovis has not been satisfactorily worked out. The asexual reproduction in the blood of the vertebrate host has been described but the cycle in the tick is practically unknown.