70 SPIROCH^TES 



as was formerly only too common a frantic, terrorized city 

 helpless in the grip of a deadly yellow fever epidemic. No epi- 

 demic has occurred in the United States since 1905 and many 

 of the tropical cities, such as Havana, Manaos and Rio de Janiero, 

 which were formerly famous as endemic centers of the disease, 

 and from which it was carried to seaports in all parts of the world, 

 are now practically free from it. It is only in such notoriously 

 unsanitary cities as Merida in Yucatan and Buenaventura in 

 Colombia that yellow fever still rages, with little or no attempt 

 on the part of the inhabitants to stamp it out. 



Nature of the Disease. Our present knowledge of the nature 

 of yellow fever and of its dissemination, which has made pos- 

 sible the scientific checking of the disease and will undoubtedly 

 result ultimately in its complete extermination, is largely the 

 result of the noble and self-sacrificing work of the American 

 Yellow Fever Commission appointed in 1900, consisting of Reed, 

 Carroll, Lazear and Agramonte. Three of these illustrious men, 

 Doctors Lazear, Reed and Carroll, lost their lives directly or 

 indirectly as the result of their work, but their achievements are 

 of inestimable value to the human race and their names will 

 not soon be forgotten. The discovery by Noguchi of the organism 

 causing the disease in 1918 has opened up new possibilities in the 

 way of immunization. 



Yellow fever was shown by the American Commission to be 

 not a contagious disease, but one which can be transmitted only 

 by the yellow fever mosquito, Aedes calopus, or by injections of 

 blood from an infected person. The organism causing the disease 

 was discovered by Noguchi at Guayaquil in 1918, and was found 

 to be a spirochsete-like organism closely related to, and very 

 closely resembling, the spirochaete of infectious jaundice. It 

 was named by Noguchi Leptospira icteroides. The organism can 

 be found in the blood serum and also in the tissues of the liver, 

 kidneys and other organs. It has been obtained in pure culture 

 both from blood of patients and from inoculated animals. It is 

 an extremely delicate filament varying in length from 4 to 9 n, and 

 tapering gradually toward the extremities which end in immeas- 

 urably thin sharp points. The filament is minutely wound at 

 short and regular intervals, the length of each spiral measuring 

 about one-fourth of a micron. The windings are so placed as to 



