YELLOW FEVER 2209 
the difference between the two merely one of virulence, and may there not be 
another organism concerned in the etiology of yellow fever? 
Theiler and Sellards! continued the work and were unable to differentiate 
the two organisms by Pfeiffer’s reaction, and found guinea pigs immunized to 
one were also immune to the other, indicating serological identity of the two 
organisms. Schuffner and Mochtar ? later confirmed this work. 
Sellards * then found in the study of the blood serum of eleven patients, taken 
three and a half months after recovery from yellow fever, that Pfeiffer’s reaction 
with both L. icteroides and L. icterohaemorrhagiae was negative, while with 
guinea pigs immunized with these organisms, it was always positive. Sellards 
and Theiler further showed that the blood serum of five cases of leptospiral 
jaundice all showed a positive Pfeiffer’s reaction for considerable periods after 
recovery. 
Sellards and Gay * then showed that L. icterohaemorrhagiae and L. icteroides 
behave in a similar manner in the mosquito, Aédes aegypti. Neither strain was 
transmitted from guinea pig to guinea pig nor to human volunteers by the bite 
of this mosquito. After the ingestion of either strain by the mosquito, the 
numbers of Leptospira diminished rapidly in the first few days, then more slowly 
for several weeks, and eventually disappeared completely. 
It will be remembered that A édes aegypti had previously been shown to trans- 
mit yellow fever for at least fifty-nine days after having bitten an infected patient. 
Important discoveries with reference to yellow fever were also made in West 
Africa during 1927-1928 by Stokes, Bauer and Hudson, Klotz and Simpson, all 
working in the Rockefeller Institute, in Lagos or in Accra, and by Sellards of the 
Department of Tropical Medicine of Harvard University, and Mathis and 
Laigret of the French Medical Service at Dakar. Klotz and Simpson °® showed 
that from a pathological standpoint there is no fundamental difference between 
yellow fever as it occurs in Africa and America, the same pathological lesions 
being noted in both. JL. icterovdes was not found in the African cases. The late 
Adrian Stokes then showed that yellow fever in Africa could be transmitted to 
the monkey (Macacus rhesus), both by the inoculation of blood from human 
eases of the disease and by the bites of infected Aédes aegypti that had been pre- 
viously fed upon human cases of yellow fever. Stokes, Bauer, and Hudson ° con- 
firmed and extended this and other work by showing that mosquitoes once 
infected with the yellow fever virus remained infective for the rest of their lives, 
exceeding three months in some instances. Attempts to cultivate Leptospira or 
to find them in the tissues from animals infected with yellow fever virus, failed. 
Finally, Mathis, Sellards, and Laigret ‘ also have shown that yellow fever may 
1 Theiler and Sellards: Amer. Jour. Trop. Med. (1927), VII, 369. 
2 Schuffner and Mochtar: Arch. f. Schiffs- und Tropen-Hyg. (1927), XX XJ, 149. 
3 Sellards: Amer. Jour. Trop. Med. (1927), VII, 71. 
4 Sellards and Gay: Ann. Trop. Med. and Parasitology (1927), X XI, 321. 
5 Klotz and Simpson: Amer. Jour. Trop. Med. (1927), VII, 271. 
6 Stokes, Bauer, and Hudson: Amer. Jour. Trop. Med. (1928), VIII, 103; loc. cit., p. 261; loc. cit., 
p. 371. 
7 Mathis, Sellards, and Laigret: Comptes rendus séances Acad. d. Sciences (1928), CLX X XVI, 604, 
and see Trop. Dis. Bull. (1929), XX VI, 647; Conférence Africaine de la Fiévre Jaune (1928). 
