IMMUNITY TO TSETSE-DISEASE. 263 



fore, we must begin to build railways, if we would replace 

 the 'system of carrying loads on the heads of niggers " 

 (pp. 146-147). 



Discussion of the question of immunity, or "facultative' 

 immunity to Tsetse-fly disease (p. 148). The following is a 

 translation of the concluding sentences of this section : 

 "It was thought, hitherto, that the gray, or so-called 

 Masai donkey is immune ; but in Mombo at the foot of 

 the Usambara Mountains, the parasites of Surra have 

 been detected in the blood of Masai donkeys which fell 

 sick there. Perhaps, however, the greater number of 

 Masai donkeys are facultatively immune. At any rate, 

 the infection experiments of Koch had a negative result 

 (BeisehericUe, p. 70). It is probable that immunity 

 may also be produced artificially. Professor Koch 

 and Veterinary-Surgeon Schmidt have already made a 

 bef^inning here with experiments in this direction, while 

 experiments with a serum-treatment were recently carried 

 out by Dr. Schilling, in Togo, apparently with success. 

 (Sitzungsher. des kolonialwirtschaftlichen Komitees, 1901)." 



Veterinary-Surgeon Schmidt's vietvs as to the nature of 

 Tsetsefly disease (pp. 148-150). 



[Translation.] " Veterinary-Surgeon Schmidt has re- 

 corded his opinions on Surra in the following memorandum, 

 addressed to the Songea Station and here reproduced 

 verbatim : — 



" « 1. In a district free from Tsetse Surra cannot be 

 conveyed from one animal to another either directly or 

 indirectly. Flies and horse-flies other than the Tsetse 

 are of no importance as regards the occurrence of Surra, 

 since, analogously to all parasitic diseases, a correlation 

 exists between host, parasite, and intermediate host, so 

 that the disease is not developed if only a single one of 

 the three conditions is not fulfilled. 



"'(a) The parasite lives only in the blood of animals 

 susceptible to the disease (single- and double-hoofed 

 Ungulates),* but can be transmitted to almost all animals 

 by artificial inoculations. 



* The limitation of Tsetse-fly disease to Ungulates is not in accordance 

 with the result of Lieut.-Col. Bruce's experiment, in which the disease 

 was produced in a dog by inoculation with blood from a Mjxna (see 

 Chapter VII., Appendix A, p. 280).— E. E. A. 



