THE FIGHT AGAINST YELLOW FEVER. 345 



ment of its vital functions. The perfect insect can subsist only at 

 a temperature })etween GO and 100° F. ; below 00° it is paralyzed, 

 benumbed, it dies; at 65° it moves with difficulty. It bites with 

 ener<>:y only above 75°. It mates between (iS and 85°, but there is fer- 

 tilization only when the temi)erature is above 75°. It lays its eggs 

 in the water where it lives, in stagnant water of flower vases, gutters, 

 bottles, tubs, and sinks, but only when the temperature is from SO 

 to 85°. 



The conditions of development of tli(> larvie are not less rigorously 

 ]:>rocise. The development of the egg and the hatching of the larva 

 demand a temperature between 08 and 85° — the best is at 82°. All 

 lowering under that figure shows itself l)y a greater or less retarda- 

 tion in their development. Tlie larva is aciuatic. Its respiration of 

 air obliges it to fix itself at the surface of the water or to rise there 

 to seek the air ])eriodically. It devel()i)s nornudly into a perfect 

 insect in a period of nine days, provided the tem))erature at night 

 does not go below 80°; otherwise the fornuition of the winged insect, 

 capable of mating and of reproducing itself, is prolonged to forty or 

 even sixty days. 



To sum up, then, it appears that the yellow-fever mosquito obtains 

 its full and regular vital development only at an average tempera- 

 ture of 82°, and that any lowering of the temj^erature night or clay 

 renders less efficient some one of its physiological functions. This 

 data is consequently of the first importance. The strict dependence 

 of the mosquito on temperature conditions is an essential fact in the 

 interi:>retation of the history of yellow fever; it is the key to all its 

 .mysteries. The Stog'omyia needs plenty of heat and of heat steadily 

 maintained. As soon as the temperature falls, the insect's life be- 

 comes endangered, and at ()0° it is benumbed and soon dies. This 

 sensitive insect does everythiiii>: in its powei- to i)rotect itself from the 

 inci-easing chilliness of the air, and its mode of living offers the means 

 for doing so. It is practically a fellow-boarder with man, under the 

 same roof. It is a domestic aniinab like the house fly. AVhenever it 

 is cold, it takes refuge in kitchens, bathrooms, heated bedrooms, in 

 bakeries, or in other warm places. On shij)s it hnds a last resort 

 close to the engine room, near the heat pij^es or smok'e |)ipes. If the 

 temperature falls beloAv (U)", it becomes torpid and IxMunubed like a 

 inarriiot. 



These conditions in their rigorous jirecision are. so far as known, 

 peculiar to the Stegomyia among all mosquitoes, and explains 

 many features in the history of yellow fever. T shall mention 

 but one. This relates to the peculiar imnninity enjoyed by the 

 inhabitants of l\>tropolis, in Brazil. Petropolis may be called 

 the sanitarium of Rio Janeiro. It is a country resort 30 miles 

 SM 1905 26 



