12 



YELLOW FEVER PROPHYLAXIS IN NEW ORLEANS 



mosquito is often called the " Tiger Mosquito." The females only 

 suck blood, and they appear to attack man both during the day and 

 at night ; between 4 p.m. and midnight is stated by some to be their 

 most active period. For this reason it is necessary to take precau- 

 tions against them at night as well as by day. The Stegomyia is 

 subject to seasonal variations, cold being the great factor in stopping 

 biting activity and breeding. Below 75°F. development is retarded, 

 and the eggs kept at a temperature of 68°F. do not hatch. It is for 

 this reason that the onset of cold weather m New Orleans soon puts 

 an end to Yellow Fever, and that the City is said to enjoy a natural 

 immunity from December to May. Too much stress must not be laid 

 upon this, however, as the fact remains that the mosquito readily 

 survives through the winter. The distribution and history of this 

 mosquito during these months require close investigation, and I trust 

 that again the New Orleans Medical Society will take the matter up. 

 Each female lays between 20 and 75 eggs on the surface of the water ; 

 these are minute, black and cigar-shaped ; they are very resistant, 

 and have been kept in the dry state for periods varying between 10 

 and 20 days, and freezing does not destroy their fertility. The eggs 

 are, therefore, a ready means of tiding over the cold weather. Under 

 suitable conditions of temperature the eggs hatch out, according to 

 different observers in from 10 hours to 3 days. The result is the 

 well-known " wiggle waggle," or " wiggle tails," the larval stage of 

 the mosquito. The larvae are very active and very sensitive, and 

 very rapidly disappear from the surface of the water in the cistern if 

 the least disturbance occurs. For this reason the water-barrel or vat 

 must be approached gently if one is desirous of obtaming specimens 

 and examining them, otherwise they wriggle very rapidly to the 

 bottom. Another point has also to be borne in mind, and that is, 

 that they cling to the sides of the receptacle and hide in the crevices 

 so that it is by no means easy to get rid of them. Simply emptying 

 the water out of the receptacle will not suffice ; a very thorough 

 rinsing and cleaning is necessary. The duration of the larval period 

 is from 6^ to 8 days normally ; but, of course, they may remain in 

 the larval stage for a much longer period ; for instance, I brought 

 some specimens alive to Liverpool which I collected at Puerto Barrios 

 in Guatemala, on October 26th. They were kept in a large test tube 

 either in my pocket or in my living room, and they were exposed to 



