A. Balfour 
261 
I merely made a mental note of this finding, telling Dr Wenyon 
about it when he visited Khartoum , but though I subsequently examined 
the blood of hundreds of gerbils in connection with trypanosome and 
other work I never saw anything like this particular parasite again 
until Captain Archibald several years later one day came across a 
solitary example of what was evidently the same flagellate in the blood 
of another gerbil of the same species. 
Its appearance and movements in the coverslip preparation having 
been duly noted, the cover glass was slipped off, the blood allowed to 
dry on it and the slide and the films carefully stained in the confident 
expectation that its morphology would now be fully revealed. 
Strange to say the parasite could not be found despite prolonged 
and repeated search. The gerbil was sacrificed but its further examina¬ 
tion yielded no results. Although I am not prepared to say this 
flagellate was an herpetomonad I am inclined to think it may have 
been after reading the descriptions given by Fantham, Porter, Dutton 
and Todd. It is interesting to note that the two former authors were 
unable to obtain stained preparations of the herpetomonads in the 
blood of their mice and that Dutton and Todd speak of their parasites 
sometimes assuming an “S ’’-shaped form. It may be that the hooked 
form of one extremity of the flagellate I first saw was due to a movement 
of this nature. 
I believe that this parasite in the blood of gerbils was not due to 
any accidental contamination, but one must remember this possibility 
both as regards faecal and seminal contamination. It is curious that 
Captain Archibald’s experience was nearly identical with mine. We 
decided to say nothing about it as we fully expected to encounter the 
parasite again, but this did not prove to be the case. 
In the light of Fantham and Porter’s communication, however, it 
now seems advisable to mention the occurrence of this peculiar and 
rare flagellate in the peripheral blood of gerbils in the Sudan, as further 
search may again reveal its presence and enable some other observer 
to come to a definite conclusion regarding it. 
The flea most commonly found both on gerbils and jerboas in the 
Sudan is Pulex cleopatrae, and it was in this species of flea that in 1906 
I found herpetomonas infection to be common, as described in the 
Journal of Hygiene, 1906, vol. vi, No. 5, and subsequently in the Second 
Report of the Khartoum Laboratories. 
Parasitology vdi 
17 
