10 



mitting the parasite to a mosquito by feeding it with sirup in which 

 the body of an infected insect had been crushed. 



Judging from the variations in the virulence of different epidemics 

 it is fair to infer that there is a corresponding variation in the viru- 

 lence of the parasite. The variation in severity of individual cases 

 appears, however, to be largely influenced by the susceptibility or 

 resistance of the subject, for the bite of the same mosquito or mos- 

 quitoes will be followed in one instance by a severe and in another by 

 a mild attack. Nor does there appear to be any appreciable difference 

 in severity between attacks induced by the bite of a single as com- 

 pared with those induced by the bites of several insects. 



Susceptibility.— Attempts to induce the disease in the ordinary lab- 

 oratory animals have been unsuccessful. Marchoux and Simond (1 906a) 

 caused a mild febrile attack in one orang-outang and in one chimpan- 

 zee by bites of infected mosquitoes. Thomas (1907) induced a mild 

 febrile attack with albuminuria in a chimpanzee following an inocula- 

 tion by infected mosquitoes. 



All persons are naturally susceptible, but there is a difference in the 

 degree of this susceptibility in different races. Thus the mortality in 

 the negro is less than in the Caucasian. Age has a distinct influence 

 on susceptibility, as is shown by the mildness of attack and relatively 

 low mortality in children. Nativity and long-continued residence in 

 an endemic focus were supposed at one time to "acclimatize" and thus 

 protect against the disease, but it is now believed that this protection 

 was obtained not by the occult influence of climate but by having 

 had during childhood or at some other age a mild and unrecognized 

 attack of the disease. 



THE YELLOW IE VEE MOSQUITO. 



This insect has been known by a variety of names of which Culex 

 mosquito, Culex tseniatus, and Culex fasciatus were in most common 

 use up to 1901. In that year Theobald, having observed that some 

 sixteen species of Culex, while agreeing amongst themselves, differed 

 from the others of this genus in certain peculiarities of scale arrange- 

 ment, separated these into a group to which he applied the name 

 Stegomyia. In this group was included the yellow-fever mosquito 

 whose name thereupon became Stegomyia fasciata. Blanchard (1905), 

 however, has pointed out that the specific designation fasciata is not 

 applicable to this insect, as it had first been applied to another, so that 

 calqpus, suggested by Meigen in 1818, has the right of priority. There- 

 fore, under the rules of zoological nomenclature, the correct name is 

 Stegomyia calopus (Meigen, 1818) Blanchard, 1905. 



Adult. — The Stegomyia calopus (figs. 1 and 2) is readily recognized. 

 It is a handsome' insect — a study in black and white. The distinction 



