(2.) The discovery of the protozoa of Texas fever by Smith. In this case ticks (Rhipicephalus (boophilus) annulatus) convey the disease.
(3.) The discovery of the trypanosoma of the tsetse disease, which is conveyed by a stinging fly (Glossina morsitans).
These discoveries were followed by numerous others indicating protozoa as causes of disease.
The trypanosomata are morphologically distinguished by the existence of a flagellum. When fresh blood is examined it is scarcely possible to overlook the protozoa in the preparation, for attention is at once attracted by the energetic way in which the red blood corpuscles are continually being displaced. The peculiar form of the protozoa, however, can only be detected in stained preparations. Romanowsky’s staining method is probably the best. Trypanosomata stained by this method show a fish-shaped body, the front end of which carries a flagellum. The body of the trypanosoma is coloured blue. At the anterior end may be seen a red-stained nucleus; at the opposite end a much smaller red spot, which has been termed the nucleolus, but is more properly described as the centrosome. From the centrosome a red thread extends along the outer margin of the body as far as the front extremity, where it becomes continuous with the flagellum.
The trypanosomata increase by longitudinal fission. The centrosome and then the nucleus divide, and finally a second flagellum is formed. Sometimes the young trypanosomata remain connected, producing the so-called “rosettes.”
The disturbance produced by trypanosomata seldom becomes acute, but often continues for years. The only sign of disease consists in ill-defined fever with long intermissions. The destruction of the red blood corpuscles causes anæmia, the animals or men become weak and waste away, œdema and sometimes erythema occur at varying points in the body, and occasionally the lymphatic glands become swollen.
The classical land of the tsetse disease is in the neighbourhood of the Zambesi. There it was seen and very well described by Livingstone; but, unfortunately, further investigations have shown that tsetse disease extends over the whole of Africa.
Whilst the trypanosomata of rats can only be conveyed to the one species, those of tsetse disease thrive in all mammals, particularly in the horse, mule, ox, dog, rat, and mouse.
The tsetse organism has been shown to kill both horses and mules, but to be less dangerous for oxen. A certain relative immunity exists in some races. As regards the ass, observers are not agreed; Koch failed to infect it. Sheep and goats are also but slightly susceptible. The conveyance of trypanosomata from the blood to uninfected animals occurs through the medium of a stinging fly (the Glossina morsitans).
Surra is endemic in the Philippines, Java, and the island of Mauritius. Koch regards the trypanosomata of surra as strictly analogous with the parasites of tsetse disease. Horses (and, in India, elephants) especially suffer from surra. Although the Glossina morsitans does not occur in India, other stinging flies replace it and convey the disease.