PROTOZOA AND DISEASE 203 



within the memory of all mature persons that the region 

 of the Panama Canal, once a hotbed of pestilence, has 

 been made healthful. In the course of the investiga- 

 tions leading up to these results, many men have suf- 

 fered illness or even death, but this does not deter medi- 

 cal investigators from taking risks which they, better 

 than any others, understand. At an early stage in the Yellow fever 

 investigation of the transmission of yellow fever in Cuba, 

 Dr. J. W. Lazear of the United States Army lost his 

 life ; but this did not prevent his colleagues, Reed, 

 Carroll, and Agramonte, from continuing the work, 

 until they had proved conclusively that this disease is 

 brought about only through the bite of a particular type 

 of mosquito, known as Stegomyia. The mosquito does not 

 itself cause the disease, but conveys the organism which 

 produces it. With this information it was easy to un- 

 derstand why yellow fever never became permanently 

 established in the North, for Stegomyia lives only in 

 warm temperature and tropical regions. It was also 

 possible to see the futility of a great deal of disinfection 

 work which had formerly been regarded as the most 

 important means of protection. A man may sleep in a 

 bed which has just harbored a yellow-fever patient, and 

 suffer no evil consequences. More especially, however, 

 it was possible to get rid of the disease by destroying the 

 breeding places of the mosquitoes, the whole yellow-fever 

 problem being thus rendered comparatively simple and 

 easy of solution. There is no longer any excuse for 

 the prevalence of yellow fever in a community. 



6. In the case of malaria (ague or swamp fever) it was Malaria 

 also found that mosquitoes were to blame, but this time 

 an entirely different kind, belonging to the genus Ano- 

 pheles. The causative organism of malaria, called Plas- 

 tnodium, is readily visible under the compound micro- 



