B. ict&roides from consideration. That the attacks of fever so 

 produced were not simply such as might be caused by the injection of 

 a soluble toxine circulating in the blood is shown by the following 

 chain of experiments: 



The first link in the chain was a fatal nonexperimental case of 

 yellow fever which furnished the Army Commission" with blood that 

 culturally showed the absence of B. icteroides, but 0.5 cc. of which 

 injected subcutaneously into a nonimmune (W. F.) a induced an attack 

 of fever having all the characters of yellow fever. From the latter 

 case blood was drawn and 1 cc. injected into a second nonimmune 

 (J. H. A.) a ; culturally this blood was sterile, but nevertheless it 

 caused an attack in all respects similar to yellow fever. Eight hours 

 after the onset of this man's illness some mosquitoes were allowed 

 to bite him, one of which, 26 days later, was applied to a nonimmune 

 (Vergara) s , who developed an attack of yellow fever 3 days, 10 hours 



later (see diagram). 



Diagram. 



Non- 



First. ' Second. Third. 



experimental Experimental Experimental Experimental 



case. . case. case. case. 



@_ -©— , <D -*© 



Induced bv injection of Induced by injection Induced by bite 



0.5 cc. blood from No. 1. of 1 cc. blood from No. of amosquito that 



Cultures from blood, no 2. Blood cultures ster- had fed on No. 3, 



B. icteroides. ile. 26 days before. 



The only possible explanation of this chain of events is that there 

 was present in the blood used for the subcutaneous injections an 

 organism that can not be cultivated on ordinary media — B. icteroides 

 grows readily on all ordinary media — and that the mosquito that bit 

 the second of the experimental cases became infected with this organ- 

 ism and 26 days later transmitted this infection to a nonimmune. It 

 is inconceivable that a toxine alone could infect a mosquito in such a 

 way as to enable the latter, 26 days later, to reproduce the disease by 

 biting a nonimmune. "It mav be observed in this connection that a 

 person who has suffered from an attack of the disease, acquired natu- 

 rally or experimentally through the bite of a mosquito, is immune to 

 injections of virulent yellow fever blood serum and, vice versa, 

 an attack of the disease induced by the injection of yellow fever 

 blood protects against subsequent inoculation by means of infected 

 mosquitoes. 



The parasite. — While the organism of yellow fever has not yet been 

 discovered, we are, nevertheless, in possession of some facts which 

 enable us'to form some idea of its character. The disease has been 

 found to occur in nature only in man and the mosquito, so that it is 



a Reed, Carroll, and Agramonte, 1901b, p. 16. 

 6Guiteras, 1901, p. 812. 



