184 YELLOW FEVER [CH 



Unless greater care is taken to screen ships during their 

 stay in infected ports, there is little doubt that occasional 

 epidemics of this nature now and then will appear. In North 

 Europe, where the absence of Stegomyia prevents any further 

 spread of the infection, these slight outbreaks are of com- 

 paratively slight danger, but in regions where the mosquito 

 is abundant, e.g. Malay and India, the introduction of a few 

 infected Stegomyia might lead to the production of terrible 

 epidemics, such as those which raged in Barcelona during 

 the eighteenth century. 



Mode of infection. The various theories as to the nature of 

 this disease have been sufficiently discussed in the previous 

 chapter, and we shall at once proceed to a description of the 

 work of the American Commission of 1899, on the transmission 

 of yellow fever 



The first attempts of this commission to transmit the 

 disease by mosquitoes were made with some Stegomyia fasciata 

 that hatched in the laboratory from eggs supplied by Finlay. 

 These insects were fed several times on patients suffering from 

 yellow fever at various stages of the illness. Eleven persons 

 having offered themselves for experiment, each day these 

 infected mosquitoes were fed on a fresh human subject. Only 

 two of these persons became infected, and both of them had 

 been bitten by mosquitoes that had fed 12 days previously on 

 the blood of a yellow fever patient in the first stage of the 

 disease. 



In this preliminary experiment the possibility of these two 

 patients having become infected by other means had not been 

 definitely excluded. It was decided, therefore, to continue 

 these experiments, after taking more rigorous precautions 

 against any external contamination. A camp was estabhshed 

 in the neighbourhood of Tuemados, on a plateau that was well 

 drained, and absolutely free from yellow fever. Twenty- 

 eight non-immune subjects, mostly Americans and Spaniards, 

 were shut up in this camp and carefully examined for several 

 days in order to make sure that none of them were infected. 

 If any of the patients shewed the slightest febrile symptoms 

 they were at once removed from the camp, but none of the 



