368 POPULAR SCIENCE MONTHLY. 



cycle of the parasite, or that it may be propagated through successive 

 generations of mosquitoes. 



It is well known that persons engaged in digging canals, railroad 

 cuts, etc., in malarious regions are especially liable to be attacked with 

 one or the other of the forms of malarial fever. This may be due to the 

 fact that the digging operations result in the formation of little pools 

 suitable for the development of the eggs of Anopheles, but another ex- 

 planation has been offered. Eoss and others have found in infected 

 mosquitoes certain bodies, described by Ross as 'black spores/ which re- 

 sist 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 have 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 other- 

 wise, gain access to the workmen engaged' (Manson). This hypothesis 

 is not supported by recent observations, which indicate that infection in 

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

 fected 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 by the microscope; but this fact has little value in view of the 

 great variety of micro-organisms present in marsh water or suspended in 

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

 recognizing the elementary reproductive bodies by which the various 

 species are maintained through successive generations. It would appear 

 that a crucial experiment for the determination of this question would 

 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 29. 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 during 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 villages in the 

 mountainous regions near the Roman Campagna and work during the 

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

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

 great risk of falling sick with fever, as a result of 'exposure to the night 

 air.' What has already been said makes it appear extremely probable 



