666 MICROBIOLOGY OF THE DISEASES OF MAN AND ANIMALS. 



the formation of agglutinins and complement-binding bodies, but these 

 have shown no practical value in treatment. 



YELLOW FEVER.* 



4 



Yellow fever is an acute infectious, non-contagious disease of man 

 which is seen in tropical and sub-tropical countries, particularly the West 

 Indies, South America, and the west coast of Africa. The most notable 

 symptoms of the disease are fever, jaundice, and haemorrhages from the 

 mucous membranes, this latter resulting in severe cases in what is known 

 as "Black Vomit," which consists chiefly of extravasated blood which 

 has been changed to a brown or black color by the action of the gastric 

 juice. 



Prior to the brilliant researches of Walter Reed and his associates 

 on the United States Army Commission in the year 1900, it was generally 

 believed that yellow fever was contagious, and that the disease was trans- 

 mitted directly from infected to non-infected individuals, and furthermore 

 that the clothing, bedding, and all materials which came in contact with 

 the infected subject were capable of transmitting the disease. Reed and 

 his associates, during the American occupation of Cuba, secured a number 

 of volunteer subjects to serve the Commission in its studies. This 

 Commission demonstrated positively that yellow fever could not be trans- 

 mitted to man in any other way than by the bite of a particular mosquito, 

 Aedes (Stegomyia) calopus (Meigen). These mosquitoes were allowed 

 to bite patients suffering from yellow fever at different stages of the dis- 

 ease. Subsequently these same mosquitoes were allowed to bite healthy 

 men at different periods of time following their application to the infected 

 individual. It was proved that the mosquito, in order to be capable of 

 conveying the disease, must bite an infected individual during the first 

 three days of the fever and at least twelve days must elapse thereafter 

 before the mosquito is capable of transmitting the disease to a susceptible 

 individual. 



These observations indicate that the mosquito acts as an intermediate 

 host and that the cause of yellow fever is probably some animal parasite 

 which passes through definite cycles of development. It was shown by 

 Reed and Carroll that the virus of yellow fever will pass through Berke- 

 feld filters and that the disease may be produced by subcutaneous inocu- 

 lation of healthy men with blood drawn from a patient during the first 



* Prepared by M. Dorset. 



