136 THE MAIN CURRENTS OF ZOOLOGY 



other way. Just as malaria is always transmitted by 

 mosquitoes of the Anopheles variety so also is yellow 

 fever carried by another mosquito of the genus 

 Stegomyia. 



In the year 1900, President McKinley appointed 

 Dr. Walter Reed (Fig. 26) as chairman of a com- 

 mittee to proceed to Havana for the study of in- 

 fectious diseases more especially yellow fever. In 

 about six months after his arrival he, with the 

 assistance of his associates, had shown that yellow 

 fever is transmitted only by the bite of a particular 

 kind of mosquito. 



Some of his results summarized are as follows: 



1. The virus or germ exists for the first three days 

 in the blood of the sick before it is capable of pro- 

 ducing infection. 



2. A mosquito of a single species Stegomyia 

 fasciata becomes infected by sucking blood from a 

 sick person, and after twelve days have elapsed (and 

 thereafter) can carry the disease. 



3. There is no other way of infection. 



Reed's work is another illustration of the power of 

 applied intelligence guided by scientific observation. 



The essential steps involved in this discovery are 

 similar to those in the investigation of malaria: 



