184 OTHER SPOROZOA 



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. 



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 " germ " lives in the blood 

 serum and not in the corpuscles, and is only infective for three 

 or four days after the appearance of the disease. It is in all 

 probability an ultra-microscopic protozoan since it can pass 

 through filters which will retain organisms on the borderland of 

 visibility and since no one has yet been successful in discovering 

 it. Numerous supposed yellow fever parasites have been found, 

 but none of them will stand the test of critical scientific exami- 

 nation. Conspicuous among these discoveries of yellow fever 

 parasites stand (1) Bacillus ideroides, discovered in the blood of 

 yellow fever patients by Savarelli and since shown to have no 

 causal relation to the disease; (2) Myxococcidium stegomyice, 

 discovered in infected yellow fever mosquitoes by a " Working 

 Party " appointed by the American Yellow Fever Institute; 

 and (3) Paraplasma flavigenum, discovered in the blood of 

 3'ellow fever patients and of experimentally infected animals 

 by Seidelin in West Africa, but also found by other workers in 

 uninfected animals and not generally accepted as the cause of the 

 disease. 



Since the mosquitoes cannot transmit the disease by biting 

 until 12 or 14 days after sucking infected blood the parasites 

 evidently undergo a cycle of development in the mosquito as do 

 the malarial parasites. The appearance and habits of the yellow 

 fever mosquito are described on page 443. 



The Disease. — Yellow fever has an incubation period of 

 from three to six days. The first symptoms are severe headache 

 and aches in the bones, followed by a sudden fever during which 

 the face is flushed and swollen and the skin dry. This fever 

 slowly subsides, and after three or four days there is a period 



