Martini, who carried out these experiments, was able to increase the 

 virulency of the mare's strain to a great extent. Dogs, injected with 

 virus of the first generation, only died after 100 days ; bvit dogs injected 

 with virus from later generations died in 10-15 days. It was also noticed 

 that dogs which had recovered from an infection with the earlier genera- 

 tions died from the infection when injected with a later generation. Here 

 no immunity was observed. 



Conclusion. 



(1) The two strains of the stallion and the mare had for morphological 



and other reasons to be considered identical. 



(2) They were of different virulency. 



(3) The virulency could by passage be so increased that the immunity 



obtained from one virus, low in the scale of generations, did not 

 protect against the same virus higher in the scale. 



Koch* has made some further observations which are useful from 

 our point of view : Two head of cattle which had been inoculated with 

 an attenuated strain of trypanosomes, apparently recovered, inasmuch 

 as in their blood microscopically trypanosomes could no longer be seen. 

 They were tested, together with some control animals with a virulent 

 strain of trypanosomes. The controls showed the disease in the usual 

 way ; the two vaccinated animals showed trypanosomes only for a few 

 days and remained healthy. Apparently by the first inoculation they 

 acquired some immunity against the second strain. One of these animals 

 remained for about six years under observation and was tested during 

 this time on its immunity, again with positive results. After six years 

 the blood of this animal which on microscopical examination proved to 

 be sterile was tested on dogs, when the presence of trypanosomes was 

 promptly proved. Thus in this instance we have a proof that cattle, 

 although resisting to repeated inoculation of virulent blood and therefore 

 apparently immune, can retain the trypanosome in the blood stream. 



BrucCjf who studied the Nagana in Zululand in order to trace the 

 connection between game and Nagana, inoculated the blood of game into 

 dogs, which were kept outside of the infected area (on the Lebombo 

 mountains). Thus the blood of 8 buffaloes proved to be infective 

 once ; of 13 wildebeeste three times ; of 4 koedoes three times ; and 

 once the blood of a bushbuck and a hyena. This fact demonstrates the 

 connection between game, fly, and disease in stock. 



Conclusion. 



(1) An animal proved to be immune against the inoculation of 



Nagana, but its blood proved to be virulent for susceptible cattle. 



(2) Game, which are considered immune against Nagana, may carry 



the infection in their blood. 



* Loco cit. 



f Further Report on the Tsetse Fly Disease or Nagana of Zululand. 



