95 



JoHNSOx (C. W.). On the Variation of Tahanus aimtus, Fabricius. — 

 Psijche, Boston, Mass., xxvi, no. 6, December 1919, pp. 103-165. 



Tahanus atratus, F., which is distributed along the Atlantic coast 

 from Maine to Florida is subject to considerable variation, but this 

 is apparently confined to the immediate seaboard, where the species 

 probably breeds in brackish marshes. Tahanus nantuckensis, Hine, 

 which is apparently confined to the New England coast, is only a 

 variety of T. atratus, another being T. atratus vsiv.fulvipilosus, var. n., 

 from Florida and New Jersey. 



Similar though less pronounced variations occur in Tahanus trispilus 

 and Ch rt/sojjs faliginosus. 



Ludlow (C. S.). New Mosquitos from Panama. — Psyche, Boston, 

 Mass., xxvi, no. 6, December 1919, pp. 166-169. 



The new species, described from the females only, are : — Anopheles 

 {Stethomyia ?) niveopaljns, and Trichoprosopon {Johlotia) shropshirei. 



Carter (H. R.). The Mechanism of the Spontaneous Elimination of 

 Yellow Fever from Endemic Centres. — Ann. Trop. Med. Parasit., 

 Liverpool, xiii, no. 4, 15th March 1920, pp. 299-311. 



In tropical America, yellow fever is eliminated north and south of 

 a central zone by the death or inactivity of Stegomyia due to cold 

 weather. It has also been ehminated in places within the zone by 

 sanitary measures. In the latter case the destruction of Stegomyia 

 is not absolute. If the number of mosquitos is brought below the 

 " critical number " for yellow fever, the disease dies out. This 

 number varies directly as the proportion of individuals immune to 

 yellow fever to the total population. But in a large number of places 

 in the zone yellow fever has disappeared for a number of years or 

 entirely, though no sanitary measures were taken, and the question 

 arises as to what the mechanism of tiiis spontaneous ehmination may 

 be. 



The parasites occur only in an infected mosquito during its Hfe 

 (say ten days), and in man for only a short time while his blood is 

 infective to mosquitos. Consequently susceptible persons are neces- 

 sary for the continuance of the disease. If yellow fever produces in 

 general a permanent immunity (to a rather less degree this will be true 

 of only a temporary immunity) the disease will eventually be ehminated 

 from a community by the failure of the human host, unless there is a 

 sufficient number of susceptible new-comers (immigrants or infants) 

 for its continuation. 



Yellow fever may obviously be introduced again into such a 

 community after the proportion of immune persons has become 

 smaller, but there seems to be no evidence of the existence of any 

 reservoirs, analogous to those that occur in trypanosomiasis, though 

 isolation from infected places is necessary. Ehmination by insect 

 control, unless it becomes more and more intensive, is subject to the 

 same objection. As the proportion of susceptible persons increases, 

 a greater destruction of Stegomyia is necessary to keep a town free from 



