18 NATURAL HISTORY OF SLEEPING SICKNESS 



were an accident, and many close allies of Trypanosomes 

 can do perfectly well without it. 



Trypanosomes of fishes are carried by leeches ^ ; of birds, 

 by mosquitoes ; those of mammals by various blood- 

 sucking insects. Thus, the rat Trypanosome is trans- 

 mitted by the rat flea, the species causing " Surra " 

 in animals by the large flies often called " Cleggs " 

 {Tabanidce), and those causing " Nagana " in animals 

 and Sleeping Sickness in man are carried by Tse-tse 

 flies (Glossina). 



The Trypanosome of " Dourine " is particularly interest- 

 ing, because it seems to have found that it can do without 

 an intermediate insect host, and is transmitted directly 

 from male to female animal, thus having severed all 

 relations with the ancestral home ! 



It may be pointed out that there is a close analogy 

 shown by Spirochaetal diseases of man, some of which 

 are carried by an intermediate host while others are not ; 

 the pathology of the two classes also shows much in 

 common, which is not surprising, considering how closely 

 allied are Trypanosomes and Spirochsetes. 



Lastly, the very interesting species which causes in- 

 flammation of the thyroid gland with fever in Brazil, is 

 carried by an insect {Conorhinus) of the order Hemiptera 

 or " bugs," an order which numbers extremely few 

 blood-suckers among its ranks, although all are adapted 

 for obtaining food by suction. Darwin made special 

 mention of this bug in his journal, and remarks that 

 " one feast kept it fat during four whole months." ^ 



The Tse-tse fUes will now be dealt with more fully, 

 but in this chapter I will only give a general account, 

 reserving a full account of the natural history of Olosaina 

 palpalis for another chapter. 



' See Miss M. Robertson's paper in Phii. Trans. Royal Soc, 1911, 

 Series B, vol. 202, pp. 29-50. 



* Voyage round the World, edition 1890, p. 316. 



