On Nag ana, or Tsetse Fly Disease. 101 



A single hedgehog inoculated was readily infected and died in seven- 

 teen days, so that this animal probably possesses a high susceptibility. 



A single donkey was inoculated and was killed twelve weeks later, 

 being then in a weak condition and near dying. 



Two horses have been inoculated, one a strong and well-fed cart 

 horse (" Russian "), which survived seven weeks, the other a rather old 

 animal (see under zebra hybrids) which survived only eight days. 



A bosch-bok has also been inoculated ; it died seven months afterwards 

 without showing any lesions. All the inoculations made from it proved 

 negative. 



Two hybrids of zebra and horse ( $ zebra and $ horse, and < horse 

 and $ zebra) and one hybrid of zebra and ass (ass $ and $ zebra) 

 have also been inoculated. These were kindly put at the disposal of 

 the Royal Society by Professor Cossar Ewart, of Edinburgh, in order 

 to see whether such hybrids are refractory to nagana. 



The two former were infected by plunging a needle wetted with 

 nagana blood beneath the skin ; the latter received a dose of 1 cubic 

 centimetre of the same blood. All of them died in about eight weeks. 

 During the course of the disease they showed irregular rises of tem- 

 perature, sometimes up to 41 '6 C. Variations in the number of 

 hsematozoa were ascertained in the case of the horse hybrids ; on some 

 occasions they were abundant (66,000 per cubic millimetre). When- 

 ever the donkey hybrid was examined at the earlier stage of the illness 

 the hsematozoa were found to be either scanty or absent. A horse 

 which was inoculated as a control died in eight days, with very abun- 

 dant hsematozoa in its blood; this animal must have been peculiarly 

 susceptible to nagana, as no other cause for death could be found at 

 postmortem examination. There is no reason for supposing that the 

 hybrids exhibited any more refractoriness than other horses or asses. 



Koch*" reports on attempts which he made to infect two Masai 

 donkeys, and two crosses from Muscat and Masai donkeys. None of 

 these showed any symptoms of the disease up to three and a half 

 months, nor were hsematozoa discovered in their blood at any time, 

 although repeated examinations were made. Consequently there is no 

 proof that these animals were really infected. In our experience 

 scratch inoculations sometimes, though rarely, fail ; on the other hand, 

 inoculations by puncture with a needle or by actual injection do not 

 fail ; Koch's animals were inoculated by the scratch method. It should 

 be added that all his control infections were successful. He did not 

 find that ordinary mules showed any immunity. 



With regard to (juinea-pigs, at first we thought that they were refrac- 

 tory under normal conditions, and that it was possible to infect them 

 only after their resistance had been reduced by bleeding or other inter- 

 ferences. 



* ' Eeisebericlite,' pp. 69 and 88. 



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