WHAT MEDICINE HAS DONE AND IS DOING FOR THE RACE 435 



and still in the incubation stage, namely the interval that 

 elapses between the bite and the onset of symptoms, and so 

 averted the distressingly fatal disease hydrophobia. The 

 success of protective vaccination with the killed micro- 

 organisms responsible for typhoid and paratyphoid fevers 

 was shown in the European War ( 19 14-19 1 8) by the freedom 

 from these diseases, unparalleled in previous wars, by the 

 troops treated with the vaccine originally introduced by 

 Almroth Wright. These are outstanding instances of infec- 

 tive diseases in which a scientific knowledge of the exciting 

 cause has enabled prevention or cure to be effected. 



Tropical medicine provides some of the most impressive 

 examples of the beneficial results of scientific investigation 

 in the prevention of disease. In 1877 Patrick Manson dis- 

 covered that mosquitoes carry and convey from man to 

 man the parasite of filarial disease, which while in the 

 mosquito undergoes a cycle in its hfe history, so that the 

 mosquito is the intermediate host necessary for the develop- 

 ment of the filarial organism and the spread of this parasitic 

 disease. The idea that blood sucking and biting flies play a 

 part in infecting man is not new; it was a behef among 

 savages, and Beauperthuy (i 807-1 871) thought it respon- 

 sible for malaria and yellow fever; Manson's suggestion 

 that the mosquito was the vector of malarial infection was 

 proved to be correct by Ronald Ross working under his 

 direction, and in 1900 Walter Reed (1851-1902) and his 

 colleagues proved the correctness of Beauperthuy and C. J. 

 Finlay's hypothesis; this was the necessary step to the 

 control and prevention of malaria and yellow fever. Similarly 

 the African sleeping sickness has been shown to be due to 

 infection with an animal parasite Trypanosoma gambiense 

 transmitted by the tsetse fly. The proof that bubonic plague, 

 due to the Bacillus pestis, is conveyed to man by the bites 

 of fleas carried by rats, and that typhus, formerly known 

 as gaol fever, is due to a rickettsia carried by lice, provided 

 an obvious guide to the prevention of these diseases. Hydatid 

 disease of the Hver and other parts (which is not a tropical 

 disease) is due to the entrance into the alimentary canal of 

 human beings of the ova of a tape worm common in the 

 intestines of dogs. 



