Probable Nature and Life Cycle of the Yellow Fever Germ 



Remarks on two Host=Parasites D 



It may seen idle to speculate about a germ which has never been 

 seen either in the blood of yellow fever patients or in the body of the 

 contaminated stegomyia, the only two sites in which we can feel certain 

 that the said germ is actually present ; yet, thanks to our present knowledge 

 of the etiology of the disease, there are many points about which very 

 plausible conjectures can be made regarding the nature and life-cycle of 

 its genu. We know, for instance, that this germ requires two special hosts 

 for the completion of its life-cycle, one of them being the body of a non- 

 immune human being and the other a particular species of mosquito; a 

 fact which at once establishes such a close analogy with the mode of 

 propagation of malaria that, unless positive proof to the contrary can be 

 brought forward, we can not forego the conclusion that the germ of yel- 

 low fever, like the germ of malaria, must be a protozoon and not a bacterium. 

 "We are, moreover, led by the same analogy to infer that the unknown germ 

 of yellow fever goes through phases of development more or less similar 

 to those of the malaria parasite which, after the original discovery and 

 patient study of the germ by Laveran, have been brought to light through 

 the genial acumen of Manson. Ross' identification of the intermediate host 

 and the minute investigations of the Italians, Grassi and Marchiafava, all 

 of which results were utilized by Koch in 1898, as the foundation for 

 practical prophylactic recommendations. 



With those data to start upon and bearing in mind certain facts which 

 have been clinically and experimentally substantiated as well as the rules 

 which appear to govern the paratitism of protozoa (Doflein, Die Protozoen 

 als Parasiten und Krankheitserreger, 1901), I shall endeavour, in the 

 first place, to show that, while the human subject is rightly considered as 

 the permanent host for the germ of malaria, it is the stegomyia mosquito 

 and not the human subject which acts the part of a permanent host for the 

 yellow fever parasite. The short sojourn of this germ in the body of the 



1) Bevista de Medicina Tropica}, Habana, abril 1903, t. IV, p. 54, and a pamphlet. 



