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Vol. 6, 1920 PATHOLOGY: H. NOGUCHI in 
I was attached to this commission as bacteriologist, and my attention 
was particularly directed, although not wholly confined to, the possi- 
bility that the inciting microbe belonged to the group of spiral micro- 
organisms which in the last ten or twelve years have come to be regarded 
as playing a very important part in human pathology. There was already 
known, indeed, a particular spiral organism, Leptospira tcterohemorrhagtae, 
which produces a severe and sometimes fatal jaundice in man, and which 
has a wide distribution in nature — far wider, indeed, than has yellow fever. 
This spiral microbe inhabits the rat, from which animal it finds its way 
at times to human beings, who then develop the symptoms and organic 
lesions of the disease called infectious jaundice. 
I have given much attention to the spiral group of microorganisms 
for about ten years. In this period I have been enabled to devise new 
methods of cultivation, which have proven successful for species not be- 
fore cultivated in successive generations, and which have also led to the 
discovery of new species. Hence in going to Guayaquil I took with me a 
laboratory outfit complete for this line of study. 
Fortunately, I was successful in detecting in certain cases of yellow 
fever by culture methods and by guinea pig inoculation a particular spiral 
organism which I have since named Leptospira icter aides. The guinea 
pigs (and, as later studies showed, also puppies) successfully inoculated 
with the blood of yellow fever patients or with the cultures develop 
symptoms and lesions closely approximating those occurring in man and 
giving the clinical picture of the disease as usually observed. The out- 
standing signs are jaundice, hemorrhage into the lungs and stomach 
(this latter in man leads to the black vomit, so called), and albumin and 
casts in the urine. At autopsy, in the guinea pig as in man, the liver, 
kidneys, and other internal organs prove to be severely degenerated. The 
spiral organisms are, of course, recoverable from the inoculated guinea 
pigs, and with these organisms the disease is transmissible through an 
indefinite series of animals. 
Moreover, guinea pigs have been successfully infected with the spiral 
organisms by means of Stegomyia mosquitoes, the vector in nature of the 
inciting microbe from man to man, and Stegomyias fed on infected guinea 
pigs are capable of transmitting the active microbe to still other guinea 
pigs, which develop the symptoms and lesions described. 
Finally, immunological studies have brought out important points of 
relationship (for example, to the Leptospira of infectious jaundice) and 
indicated the possibility of developing a "vaccine," and even a curative 
serum. But until the finding of Leptospira icteroides is confirmed by the 
investigation of cases of yellow fever in still other places, its standing as 
the inciting agent of yellow fever will have to be regarded as not yet cer- 
tainly established. 
