MALAEIA. (553 



the other of the forms of malarial fever. This may he due to the fact 

 that the dig-g-ing- operations result in the formation'of little pools suit- 

 able for the development of the eggs of Anopheles; but another explana- 

 tion has been offered. Ross and others have found in infected mos- 

 quitoes certain bodies, described by Ross as " black spores," which resist 

 decomposition and which may be resting spores capable of retaining their 

 vitality for a long time. The suggestion is that these "black spores" 

 or other encysted reproductive bodies may ha^ve been deposited in the 

 soil by mosquitoes long since defunct, "and that in moving the soil these 

 dormant parasites are set at liberty, and so in air, in water, or otherwise 

 gain access to the workmen engaged" (Manson). This hypothesis is 

 not supported by recent observations, w^hich indicate that infection in 

 man occurs only as a result of inoculation through the bite of an 

 infected mosquito. The question is whether malarial fevers can be con- 

 tracted in marshy localities independently of the mosquito, which has 

 been demonstrated to be an intermediate host of the malarial parasite? 

 Is this parasite present in the air or water in such localities, as well as in 

 the bodies of infected mosquitoes ? Its presence has never been demon- 

 strated b}" the microscope; but this fact has little value in view of the 

 great variety of microorganisms present in marsh water or suspended in 

 the air everywhere near the surface of the ground, and the difficulty of 

 recognizing the elementar}- reproductive bodies b}^ which the \'arious 

 species are maintained through successive generations. It would appear 

 that a crucial experiment for the determination of this question woukl 

 be to expose healthy individuals in a malarious region and to exclude the 

 mosquito by some appropriate means. This experiment has been made 

 during the past summer, and the result up to the present time has been 

 reported by Manson in the London Lancet of September 2H. Five 

 healthy individuals have lived in a hut on the Roman Campagna since 

 early in the month of July. They have been protected against mosquito 

 bites by mosquito-netting screens in the doors and windows and by mos- 

 quito bars over the beds. They go about freely dui-ing the daytime, 

 but remain in their protected hut from sunset to sunrise. At the time 

 Manson made his report all these individuals remained in perfect health. 

 It has long been known that laborers could come from the A-illages in the 

 mountainous regions near the Roman Campagna and work during the 

 day, returning to their homes at night, without great danger of contract- 

 ino- the fever, while those who remained on the Campagna at night ran 

 o-reat risk of falling sick with fever, as a result of "exposure to the night 

 air " What has already been said uiakes it appear extremely probal.le 

 that the " night air," per se, is no more dangerous than the day air, but 

 that the real danger consists in the presence of infected mosquitoes of 

 a species which seeks its food at night. As- pointed out by King, in 

 his paper alreadv referred to, it has repeatedly l>een claimed by 

 travelers in malarious regions that sleeping under a nios,|u.to bar is an 

 effectual method of prophylaxis against intermittent fevers. 



