Before 1900, many theories existed as to the cause of yellow fever  . Some doctors were sure the disease was air-borne; others felt that it was spread from person to person. Dr. Carlos Finlay, a well-known Cuban doctor of that time, had long held the theory that it was caused by the bite of mosquitoes. But neither the public nor the doctors then accepted his idea.    Walter Reed,all American doctor sent to study yellow fever in Cuba,went to talk with Finlay.Reed,after reading a lot on the subject,had begun to think that Dr.Finlay might be fight.Then Reed and his comrades set to work at once.Outside Havana,they set up a laboratory and began experiments to test the theory.The experiments were successful.Now we know:A period of about two weeks must pass before a mosquito,after feeding on a sick person,could infect  another person.The sick person had to have yellow fever a certain number of days before the mosquito biting him was able to carry the disease. Reed proved the theory  _  .
in his American lab by talking with Finlay in a kind of scientific Way by reading a lot of articles