552 

 "Traite de Botanique" i París, 1884, p. 88) considers critical for seels and 



plants, namely: 



N.° 1. A low temperature-limit, In-low which the external manifestations 



of life are suspended although vitality persists ill a latent condition. 



I have observed this to occur with the Havana stegomyia when the 



temperature is lowered to between 15 C and 19° C. This would be 



the limit for "apparent death by cold." 



N.° 2. A high temperature-limit, above which the stegomyia drops into a 



state of letharge, apparently dead, hut may completely revive in 



a lower temperature This is observed to happen when the 



temperature is raised to 37° or 38° C. This is "apparent death 



by heat." 



X." 3. An intermediate temperature-limit, at some point between N. 1 



and N.° 2, at which all the vital fuctions are accomplished in the 



most perfect manner. This optimum-limit 1 have not been able to 



determine in the adult insect; but taking as a criterion the mean 



temperature of days when the succesive phases of development, 



from the ovum to the imago, are most rapidly accomplished, I am 



inclined to place this limit at some point between 2!)° and 31° C. 



These being also the mean temperatures which are most frequently 



recorded during the acme of severe epidemics. 



N.° 4. A still lower temperature, below N.° 1, at which life ceases 



altogether; this being "real death by cold". I have observed it, in 



Havana, when the temperature was artificially lowered to I o C. or 



4° C. 



N.° 5. A high temperature-limit, above X.'' 2. at which life is also 



completely extinguished beyond the possibility of revival. This is 



the limit of "real death by heat", which I have observed in some of 



my experiments during the winter season, when the temperature 



was raised to between 39° and 40° C. 



But the five temperature-limits scheduled above leave entirely out of 



consideration precisely the two most essential ones so far as the 



transmission of yellow fever and the multiplication of the transmitting 



insect are concerned. I refer to the temperature-limits below and above 



which the stegomyia may be unable to bite and to suck blood. It might be 



thought that almost simultaneously with the recovery of its general motility. 



after having been previosly benumbed by excess of heat or of cold, a 



stegomyia which is seen to fly and to move about with ease or to feed readily 



on sugar or sweet juices, would be aliso in a condition to bite and to suck 



blood. But my personal observations have long since satisfied me that this 



is not always the case. I have seen occasionally in Havana, during the 



winter season, stegomyias Hying about in the room and others, in captivity. 



feeding on sugar and flying when the temperature was not above 22° C. I 



have also seen them drive their sting as far as it could reach into the skin, 



