YELLOW FEVER 561 



by Ricketts and Wilder, 1 both in the blood of patients and in the 

 intestinal contents of lice which had been permitted to bite these 

 patients. 



The injection of cultures of the Plotz bacillus into guinea-pigs 

 resulted after an incubation period of from twenty-four to forty- 

 eight hours in a febrile reaction which dropped by lysis after four to 

 five days. This organism, Bacillus typhi-exanthematicus, as it has 

 been named, must be regarded tentatively as the etiological factor 

 of typhus fever. 



Typhus is transmitted by the body louse Pediculus vestimenti, as 

 was shown by Nicolle, Anderson and Goldberger, and Ricketts and 

 Wilder. 



Yellow Fever. Yellow fever is an acute fever of tropical and sub- 

 tropical countries, characterized by jaundice, albuminuria, and a 

 tendency to hemorrhage from mucous membranes; the latter is 

 especially marked in the stomach and the " black vomit" which occurs 

 frequently is a regurgitation of altered blood which has collected in 

 the stomach. 



For many years the etiology and mode of transmission of yellow 

 fever were wholly unknown, although many and divers organisms were 

 reported as the inciting factor. Finlay, 2 as early as 1882, believed 

 that mosquitoes played an important part in the transmission of the 

 disease and he actually attempted to infect non-immunes by mos- 

 quitoes which had previously bitten yellow fever patients. His 

 experiments were wholly negative, partly because the extrinsic cycle 

 of development in the insect was unknown. Carter 3 made the very 

 important observation that a latent period of about two weeks elapses 

 between primary and secondary cases of yellow fever. This discovery 

 explained some of Fin lay's negative results and paved the way for the 

 success of the American Yellow Fever Commission. Finally Reed, 

 Carroll, Agramonte and Lazear, 4 a commission appointed from the 

 Medical Corps of the United States Army, carried out a series of 

 experiments never excelled from a scientific standpoint, which showed 

 conclusively : 



1. The virus of yellow fever circulates in the blood stream of a 

 patient at least three days after the initial chill. An injection of blood 



1 Jour. Am. Med. Assn., 1910, liv, 1373. 



2 Ibid., 1901, xxxvii, 1387. 



3 Public Health Rep., 1905, xx, 1350; New York Med. Rec., 1906, .Ixix, 683. 



4 Jour. Exp. Med., 1900, v, 215; Am. Public Health Assn., 1900, xxvi, 37; Boston 

 Med. and Surg. Jour., 1901, No. 14; Jour. Am. Med. Assn., 1901, xxxvi, 413. 



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