u 



sudanense. Morphologically speaking, these various parasites could not 

 with absolute certainty be separated from each other, although for epidemio- 

 logical and geographical reasons a difference between Trypanosoma 

 evansi and hrucei suggested itself. French scientists introduced a method 

 of differentiation, based on the observation, that animals which recovered 

 from a trypanosome infection are immune against that particular strain of 

 virus. The duality of Trypanosoma evansi and brucei was decided in the 

 following way : * 



Laveran and Mesnil made use of two goats, which had recovered 

 from mai de caderas {Trypanosoma equinum) whose blood had proved to 

 be sterile by tests on susceptible animals. They were then injected with 

 Trypanosoma brucei, developed the disease and recovered ; thus proymg 

 that recovery from mal de caderas does not cause immimity against 

 nagana. 



One of the recovered goats was re-injected with the Trypanosoma 

 hrucei, and since no development followed it had to be concluded that 

 immunity was estabhshed. The goats were now injected with the 

 trypanosome of surra ; they both developed the disease and the presence 

 of parasites could be demonstrated by sub-inoculation into mice. 



Conclusion. — (1) Recovery of goats from nagana gave immunity 

 against the strain by which the immunity was caused. 



(2) Recovery from mal de caderas did not give immunity against 



nagana or surra. 



(3) Recovery from nagana. did not cause immunity against surra. 



French scientists worked with surra of various origins, viz., a strain 

 obtained from Mauritius, another from India, and a third one from 

 Nha-trang, China, and based on the immunity re-action declared the 

 trypanosomes found in the disease "mbori" of North Africa to be identical 

 with Trypanosoma evansi. 



Vallee and Panissetf inoculated two head of cattle with surra of 

 Mauritius. After the course of a year they no longer showed trypano- 

 somes in their blood, and a subsequent inoculation with the same virus 

 proved their immunity. They then were twice in succession inoculated 

 with the trypanosome of mbori and proved refractory. Later they were 

 ■inoculated with surra from India and again proved refractory. 



Laveran experimented in the reverse order. A male goat which 

 had recovered from mbori, and whose blood had proved to be sterile was 

 first tested with the same virus and proved to be refractory. Subse- 

 quently it was inoculated with surra of Mauritius and no infection took 

 place. From this, Laveran supported the views of Vallee and Panisset 



* Compt. Bend, dcs Seances de I'Acad. de Soienci;, t, C^XXXVI, p. 1529 ; A, Laveran et P. Mesnil. 

 I Cbmptes Eendus, 27/3/05, 



