GENUS: TRYPANOSOMA 451 



immunity on the part of the sheep, this at any rate is insufficient to 

 prevent a fresh infection. 



5. SEROLOGY.— Rabinowitsch and Kempner (1899) were the first 

 to demonstrate the protective property of the serum of animals recovered 

 from trypanosome infections. They showed that 0-5 c.c. of serum 

 from a rat recovered from an infection due to T. lewisi was sufficient to 

 protect a normal rat against infection when the serum and blood containing 

 trypanosomes were inoculated at the same time. Laveran and Mesnil 

 (1901a) extended this observation, and demonstrated that if sufficient 

 serum from an animal, such as the sheep or goat, rendered immune to any 

 particular trypanosome was mixed with infective blood from another 

 animal containing the same trypanosome, normal animals inoculated 

 with the mixture did not become infected, whereas the same serum mixed 

 with another trypanosome did not protect against infection with the 

 latter. This property of the serum for destroying trypanosomes and 

 preventing infection may be retained for long periods. The serum of a 

 chronic case of sleeping sickness in man has a similar action in the case of 

 T. gamhiense, whereas the serum of a normal individual is not protective. 

 Furthermore, Laveran (19026, 1903) was the first to demonstrate that 

 normal human serum had a marked protective action when inoculated to 

 mice at the same time as either T. brucei, T. evansi, or T. equinum. The 

 normal human serum was in some cases even curative when injected into 

 animals already infected. 



Mesnil and Ringenbach (1911) showed that it had a similar action on 

 the human strain of T. brucei {T. rhodesiense). Laveran and Nattan- 

 Larrier (1912c) discovered that this reaction was far from constant, as 

 different human strains of this trypanosome behaved differently towards 

 human serum. Freshly isolated strains tended to be killed by human 

 serum, while this ceased to be the case after the strain had been subjected 

 to many passages through laboratory animals. Laveran (1915a) showed 

 that one particular strain of T. gamhiense, even after being kept for 

 twelve years in laboratory animals, still resisted normal human serum. 

 Mesnil and Blanchard (1916), however, proved that other strains of 

 T. gamhiense may lose this resistance after long periods. Conversely, 

 T. brucei may acquire a resistance not previously possessed by it after 

 many passages, as proved by Jacoby (1909). Laveran (1904a) also 

 demonstrated that the serum of the higher apes, especially the baboons 

 (Cynocephalus), behaved like human serum. Mice injected with serum 

 at the same time as T. brucei did not become infected, whereas, with 

 T. gamhiense, they were not protected. 



The serum of animals recovered from infections may have a trypano- 

 lytic or disintegrating action on the tryj^anosomes in vitro, as first shown 



