(c) Action of Human Serum.—1 c.c. of human serum cured T. rhodesiense mice in three out of four cases; on T. gambiense mice there was no appreciable effect.
Laveran and Nattan-Larrier[76] have shown the same, namely, that human sera act on T. rhodesiense, but are quite without action on T. gambiense.
(d) Trypanolytic Reactions.—Mesnil and Ringenbach[77] have also shown that the sera of animals (man, monkey and guinea-pig) infected with T. gambiense are trypanolytic for the homologous trypanosome, that is, T. gambiense, but have no action on the heterologous trypanosome, that is, T. rhodesiense.
(4) Cross Immunity Experiments.—(a) Mesnil and Ringenbach[78] immunized a monkey (Macacus rhesus) against T. gambiense. It was inoculated with T. rhodesiense on June 7, 1911; on June 27 trypanosomes appeared, the infection being slight; on July 4 it died. A control died in ten and a half days.
(b) Laveran[79] immunized a goat and mice against T. gambiense. When they had acquired a solid immunity, they were inoculated with T. rhodesiense. They became infected like the controls.
(c) Laveran and Nattan-Larrier[80] immunized a ram against T. brucei, it subsequently became infected with T. rhodesiense.
(d) Laveran[81] immunized a ram and a sheep against different strains of T. brucei. Inoculated with T. rhodesiense they both acquired acute infections and died. Conclusion: T. rhodesiense is not T. brucei.
When the converse set of experiments is tried, namely, immunizing an animal against T. rhodesiense, and then inoculating with T. gambiense, the difficulty immediately arises that it is impossible to immunize an animal against T. rhodesiense, owing to its virulence. But a partial and transitory immunity to T. rhodesiense can be obtained by treating the infected animal with drugs, such as arsenophenylglycin. The results, so far as they go, seem to show that an animal immunized against T. rhodesiense is immune not only to T. rhodesiense, but also to T. gambiense, a fact which, according to Mesnil and Léger, does not invalidate the specificity of T. rhodesiense, but tends to show that the two trypanosomes are closely related.
(5) Mode of Transmission and Reservoir.—Kinghorn has shown that T. rhodesiense is transmitted by Glossina morsitans in which it undergoes development. Kinghorn and Yorke[82] found that about 16 per cent. of the wild game examined in Northern Rhodesia was naturally infected with T. rhodesiense. The wild game examined included waterbuck, hartebeest, mpala, bushbuck and warthogs. One native dog near the Nyasaland border was found infected, but not domestic stock. Taute doubts whether T. rhodesiense really occurs in wild game. Approximately 3·5 per cent. of the tsetse flies fed on infected animals may become permanently infected with T. rhodesiense, and capable of infecting clean animals. Furthermore, a tsetse fly when once infective probably remains infective for the rest of its life.