INTRODUCTORY 3 



As the result of the zeal of workers abroad, we have now more 

 definite knowledge of the infectious diseases more or less peculiar 

 to the tropics than we have of our own fevers. It may be asked 

 whether this is because the parasites that cause disease in the tropics 

 are larger or, like the flagellates, more readily recognised as parasites 

 than those that constitute the infections of temperate climates ; or 

 whether it may be that the conditions of investigation are better in 

 India and other British colonies than they are at home. In spite 

 of the work that has been done, the nature of the infection of some 

 tropical diseases still demands elucidation. Dengue, a fever com- 

 pared to influenza by Manson, and yellow fever are still under investi- 

 gation. The position of the pathology of yellow fever is particularly 

 interesting. It has been established, mainly by the late Walter 

 Reed, Major in the American Army, that the Stegomeia fasciata, a 

 gnat which breeds chiefly about houses, is the sole carrier of the 

 disease ; and by covering water-butts and preventing chance collec- 

 tions of water these gnats are kept down and the spread of the 

 disease is stopped. By these simple measures this disease has been 

 practically stamped out in many seaports and other places previously 

 notorious for it. 1 



Among the ectoparasites that carry protozoan and other infective 

 diseases, ticks of various kinds have recently been shown to play a 

 more important part than was previously suspected. A tick was 

 mentioned in Part I. as the carrier of the destructive cattle disease 

 caused by a piroplasma. Recently an important advance has been 

 made in our knowledge of the piroplasmata by Christophers, 2 who 

 has traced the complete life-history of P. canis, as observed in India, 

 the more important part of the parasite's life being passed in the gut 

 and tissues of a tick. 



Tick-fever is a name given to the African remittent fever, which, 

 like the European fever of the same name, is associated with 



1 The whole history of yellow fever emphasizes the immense value of a new 

 idea which is at the same time a rational induction based upon wide observation. 

 Without Hanson's 'mosquito-malaria' theory neither our knowledge of the mode 

 of convection of malaria nor that of yellow fever would have become known. 



2 S. R. Christophers, Brit. Med.Journ., January 12, 1907. 



I 2 



