382 



PSYCHE. 



contaminated by stinging a yellow-fever 

 patient (or perhaps by contact with or 

 feeding from his discharges), but may 

 be likewise inherited by the next gener- 

 ation of mosquitoes issued from the con- 

 taminated parent. With this new 

 development, indeed, the theory seems 

 to cover the whole ground of conditions 

 which are known to govern the trans- 

 mission or non-transmission of the 

 disease, and to account for everv well 

 authenticated fact on record. 



There are different species of mos- 

 quitoes which are peculiar to certain 

 localities, even within the yellow-fever 

 zone, though we are not able to account 

 for their preferences in this respect, nor 

 for the circumstances which determine 

 their pcrm;inency in such iimiteil areas. 

 It is a fact, however, that the " domes- 

 tic mosquito" (by which term I mean 

 such species as constitute a parasite and 

 commensal of man) shows no inclina- 

 tion whatever for extensive excursion so 

 long as the female insects find at hand 

 convenient subjects from whom they 

 can draw the warm life-blood which 

 they apparently require, not so much 

 for their own nourishment as for the 

 purposes of ovulation and for the repro- 

 duction of their species. That the 

 tropical species cannot well establish 

 themselves in temperate or cold cli- 

 mates, will be readily understood by 

 repeating the following experiments: 

 Let a mosquito of the small diurnal 

 species found in Havana be introduced 

 into a test tube provided with a ther- 

 mometer ; if the temperature be low- 

 ered, it will he seen that, when it falls 



to between 15° and 19° C. (59° and 

 66.2° F.), the insect becomes benumbed, 

 and unless it finds some object upon 

 which it can fasten its claws it will drop 

 to the bottom of the tube, in a condition 

 of apparent death, in which it will re- 

 main so long as the temperature is kept 

 between i5°ando°C (59° and 32°F.). 

 On allowing the temperature to rise 

 again, when it reaches above 15° to 19° 

 C the mosquito will gradually revive 

 and soon recovers its normal agility and 

 the power of stinging. On the other 

 hand, if the mosquito is confined in a 

 closed tube and the air gradually rare- 

 fied, the insect appears to lose the 

 power of supporting itself on its wings, 

 and also that of stifiening its proboscis 

 foi- the piupose of stinging. With tem- 

 peratures below 2^° C. (77° P.), the 

 time required bv the culex mosquito to 

 digest the blood and get ready for 

 another bite is prolonged to several 

 (lavs; and, according to my observa- 

 tions, the pupae of that species, if kept 

 at temperatures below 23° C. give five 

 males to one female, whereas at 25°-3o'^ 

 C, the proportions are reversed. Hence 

 it follows that during the cold season in 

 Havana there are comparatively few 

 mosquitoes of that kind in a condition 

 to propagate the vellow fever. At sea 

 mosquitoes will save themselves from 

 being blown into the water only bv 

 avoiding the deck and other exposed 

 parts of a vessel, and in travelling 

 toward cooler regions tiuy will have an 

 adilitional motive for seeking refuse in 

 the warmer and more sheltered parts of 

 the ship. Hence the likelihooij of 



