(2) _Animal Reactions._--The posterior nuclear trypanosomes were found in all sub-inoculated animals, such as rats, guinea-pigs, dogs, mice, Macacus, rabbits and horses, but were not seen in the human patient, as few trypanosomes occurred in his peripheral blood. R. Ross and D. Thomson[71] found a periodic, cyclical variation in the number of the parasites in the patient’s blood from day to day, the cyclical period being about a week (fig. 32). Fantham and J. G. Thomson[72] (1911) found a similar periodic, cyclical variation in the trypanosomes in the blood of sub-inoculated rats, guinea-pigs and rabbits. On counting the parasites in the blood of similar animals inoculated with _T. gambiense_, they established, by enumerative methods, that _T. rhodesiense_ was more virulent than _T. gambiense_, while Yorke also showed this marked virulence of _T. rhodesiense_ in practically all laboratory animals. In other words the duration of infection in the case of _T. rhodesiense_ was shorter. It was also found that _T. rhodesiense_ was resistant to atoxyl. The patient, from whom the original strain was obtained, died about nine months after the probable date of infection. Some patients infected with _T. rhodesiense_ have died in an even shorter period, such as four or five months. [71] _Proc. Roy. Soc._, B, lxxxii, p. 411. [72] _Annals Trop. Med. and Parasitol._, iv, p. 417. In sheep and goats _T. rhodesiense_ causes an acute disease, marked by high fever, œdema of the face, and keratitis, as shown by Bevan and others, death resulting after a relatively short period. _T. gambiense_ gives rise, in these animals, to no symptoms except fever, which may be overlooked. _T. rhodesiense_ produces keratitis in dogs. [Illustration: FIG. 32.--Chart showing daily counts of number of trypanosomes per cubic millimetre of peripheral blood from a case of Rhodesian sleeping sickness. (After R. Ross and D. Thomson.)] Stannus and Yorke (1911) observed _T. rhodesiense_ in animals inoculated from a case of sleeping sickness in Nyasaland. Sir D. Bruce and his colleagues[73] have shown (1912) that _T. rhodesiense_ is the parasite usually found in man and in animals sub-inoculated from cases of sleeping sickness in Nyasaland. It has since been found in German East Africa and Portuguese East Africa, while Ellacombe has described a case from North-western Rhodesia. [73] _Proc. Roy. Soc._, B, lxxxv, p. 423. (3) _Serum Reactions._--Interesting experiments on this subject were performed during 1911 and 1912 by various French investigators. (_a_) _Action of Immune Serum_ (Mesnil and Ringenbach)[74]: (1) A goat was infected with _T. rhodesiense_. Twenty-two days later its serum mixed with _T. rhodesiense_ was injected into a mouse. Result: Protection. (2) The serum mixed with _T. gambiense_ was injected into a mouse. Result: Infection. [74] _C.R. Soc. Biol._, lxxii, p. 58.