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of these were the cause of the disease. As it was 

 generally held that the vomit and excreta of 

 patients were very infectious the Commissioners 

 next devoted their attention to the elucidation of 

 this question. Since no animals were known to 

 suffer from the disease it was necessary to find 

 persons who were willing to offer themselves for 

 experiment. Volunteers, who had never been in 

 infected districts and were therefore not immune 

 to the disease, were isolated in specially prepared, 

 ill-ventilated and ill-lighted huts, and slept for days 

 in beds freshly saturated with the discharges of 

 yellow fever patients. Yet none of them became 

 infected. By a series of such experiments the 

 Commissioners showed that the common belief that 

 these discharges were infectious was incorrect, and 

 that the disease was not spread by such means. 

 They next investigated the condition of the blood 

 and ascertained that no bacteria were present in it. 

 Nevertheless the blood, at least during the first three 

 days of the illness, if injected in very small quantities 

 into healthy persons causes the disease, and there- 

 fore some virus is present in it. This virus is so 

 minute that it will pass easily through a porcelain 

 filter capable of stopping all known bacteria. It 

 is quickly killed by drying and is destroyed in five 

 minutes by a temperature of 130 F. All these 

 important facts had to be ascertained by the 

 inoculation of healthy persons. By these researches 

 the Commissioners showed that the causal agent 



