ENTOMOLOGY 27 



a mystery, and indeed it is a mystery to-day in a measure, since, 

 although undoubtedly a disease of parasitic origin, the parasitic or- 

 ganism itself has not yet been discovered. During the summer and 

 autumn of 1900 and spring and summer of 1901 the work of a 

 commission of surgeons of the United States Army demonstrated 

 in Cuba beyond the slightest possible doubt that yellow fever is not 

 conveyed by infecting clothing of yellow-fever patients or by con- 

 tact with such patients or by proximity to them, but that it is con- 

 veyed by the bite of a certain species of mosquito known as Stego- 

 myia calopus, which abounds in regions where yellow fever is pos- 

 sible. The bite of this mosquito, however, does not convey yellow 

 fever to a healthy person until twelve days have elapsed from the 

 time when the same mosquito has bitten a person suffering with 

 the disease. It follows from this fact that by keeping yellow-fever 

 patients screened from the possibilities of mosquito bites we can 

 prevent the yellow-fever mosquito from becoming infected. It fol- 

 lows further that by preventing healthy people from being bitten 

 by mosquitoes we can keep them free from the disease even where 

 infected mosquitoes exist. And it follows still further that by the 

 adoption of remedial measures looking toward the destruction in all 

 stages of the yellow-fever mosquito we may reduce to a minimum 

 the possibilities of the transfer of the disease. After demonstrating 

 the fact, the medical officers of the Army in Cuba put these meas- 

 ures into effect, and the results were most gratifying. The health 

 of Havana immediately improved, and the general health of Cuba 

 and the industrial conditions dependent upon better sanitation have 

 continually gained since. 



The New Orleans outbreak of yellow fever in the summer of 

 1905 was quickly stopped by antimosquito measures, and it is con- 

 ceded that more than 4,000 lives were saved in that city during 

 that season by the intelligent application of measures based upon 

 the discovery of the United States Army surgeons in Cuba in 1900 

 and 1901. * 



TYPHOID FEVER. 



The principal insect agent in this spread is the common house 

 fly, and this insect is especially abundant in country houses in the 

 vicinity of stables in which horses are kept. The reason for this is 

 that the preferred food of the larvas of house flies is horse manure. 

 House flies breed in incredible numbers in a manure pile, largely 

 derived from horses. Twelve hundred house flies, and perhaps 

 more, will issue from a pound of horse manure. Ten days com- 

 pletes a generation of house flies in the summer. The number of 

 eggs laid by each female fly averages 120. Thus, under favorable 

 conditions, the offspring of a single over-wintering house fly may 

 in the course of a summer reach a figure almost beyond belief. 

 With an uncared-for pile of horse manure in the vicinity of a house, 

 therefore, flies are sure to swarm. Their number practically will 

 be limited only by breeding opportunities. They are attracted to, 

 and will lay their eggs in, human excrement. Under favorable 

 conditions they will breed, to some extent, in this excrement. They 



