376 



Marvels of Insect Life. 



Photo by] [E. Step, F.L.S. 



The Cacique. 



The huge wings, which span six and a half inches from tip to tip, are coloured deep bhie with white spots. They are highly polished 

 and give briUiant reflections. The photograph is one-fifth less than natural size. 



Another genus ^ includes the mosquitoes that are necessary agents in the pro- 

 pagation of yellow fever, which can only be transmitted by their unconscious aid. 

 Here an interval of twelve days is necessary between the biting of a fever patient 

 and the attack upon a healthy person, and during that period the germs absorbed 

 pass through certain stages which make the mosquito an efticient distributor of 

 the disease to all whose blood it samples. It was the discovery of the facts concerning 

 this species that enabled the United States Commission to extirpate yellow fever 

 from Cuba, and a few years later the experience thus gained made the completion 

 of the derelict Panama Canal works possible. It was a case of Gulliver against 

 the Lilliputians ; but no military conquest recorded in history is fit to be compared 

 with it. The French Panama Company had from fifteen to eighteen thousand labourers 

 at work, and annually lost between sixty and seventy per thousand from yellow 

 fever and malaria. At length, after fifty millions of money had been spent, the task 

 was abandoned as impossible under such difficulties. Recentl}^, Colonel Gorgas, 

 with the experience gained in Cuba and the assistance of a staff of reliable helpers, 

 cleared up the belt of land through which the canal was to run, abolishing the breeding 

 places of the gnat, screening every water- vessel, and fumigating every house with 

 sulphur and pyrethrum-powder. The enemy, whose minuteness and abundance 

 made its conquest to appear an impossibility, was routed. Yellow fever became 

 practically extinct in that region, and the Panama Canal is an accomplished fact. 



The victory over the malaria-gnat was, in a sense, more difficult, because its 

 early stages are passed in clean water which, of course, cannot be sacrificed. But 

 it is more under control because the gnat rarely flies farther than two hundred yards 

 from its breeding pools ; and if the inhabitants are dosed with three grains of quinine 

 per day, their blood is rendered poisonous to any malaria germs that may get into it. 



^ Stegomyia. 



