MANKIND AND THE INSECT 327 



Since these discoveries were made, other insects have 

 been shown to be alternate hosts of certain diseases which, 

 in the past, have caused untold suffering and loss of life. 

 A gnat or mosquito called Stegomyia calopus is in this way 

 associated with the deadly yellow fever, or " Black Jack," 

 which is endemial on the east coast of tropical America, 

 and is often carried to sub-tropical, sometimes even to 

 temperate zones, where — if the Stegomyia mosquito is 

 present — it may rage until frosts set in. The yellow 

 fever microbe is known to remain twelve days in the 

 insect before it can be passed on ; and during this interval 

 it presumably undergoes certain necessary changes. But 

 the parasite has not yet been identified, although diligent 

 search has been made. Probably it is too small to be 

 seen through any existing microscope. Nevertheless, 

 experiments have proved beyond question that the germ 

 or virus is taken up by the Stegomyia, and that after the 

 twelve- days interval the insect, by its bite, is capable of 

 infecting a healthy human being with the terrible pesti- 

 lence. By recognising this fact, and by adopting measures 

 for keeping the disease-carrying gnat at bay, yellow fever 

 has been entirely abolished in many tropical cities within 

 the last ten years. Moreover, the assured success of that 

 great enterprise, the building of the Panama Canal, is 

 chiefly due to man's new-found power to combat disease. 

 When the French essayed the work, the mortality from 

 yellow fever was appalling ; but thanks to the advance of 

 science the Americans have been able to override this 

 obstacle. Writing from the Canal zone in September 1912, 

 a journalist, Mr. J. F. Fraser, says : " Before the Americans 

 came the Isthmus was one of earth's pestiferous spots: 

 swampy, miasmatic, mosquitoes carrying yellow fever and 

 malaria. Colon was the white man's grave. Panama 

 reeked with uncleanness and disease. The interlying 



