140 MODE OF TRANSMISSION OF YELLOW FEVER 



to the fact either that cases of tlie disease are present 

 amongst the indigenous inhabitants, or that it breaks 

 out amongst a particular colony of labourers in a town 

 or district (such as amongst the Sicilians and Italians in 

 New Orleans in the year 1905, who do not readily seek 

 medical advice and are often exceedingly suspicious), or 

 that early cases are not recognised. In districts wdiere 

 malaria takes a pernicious form, or wliere dengue is 

 common, the difficulties of diagnosis must be greatly 

 increased, and experience imder these circumstances 

 M'ill be of great value. On the other hand, some other 

 epidemic may have preceded the yellow fever, and 

 cases which were in reality yellow fever may have been 

 placed to the credit of the former. 



In large cities, as mentioned in the pre\'ious chapter, 

 a clue that something unusual is happening may be 

 afforded by analysis of the weekly deatli returns. A 

 sudden rise in the number of deaths recorded from 

 malaria in a month, at a season of the year when 

 malaria has not occin-red in previous years, would be 

 a very suspicious element. In small towns, however, 

 such indication would probably be too slight to be of 

 practical \'alue in putting a community upon its guard. 



AMiere tlie practitioners themselves have had the 

 ad\'antage of previous experience in the disease there is 

 a greater chance of early notification. But 1 venture 

 to suggest that experience gained of yellow fever or any 

 other disease twenty or fourteen years previously is not 

 so valuable as experience of the disease acquired since 

 our knowledge of the disease has been very greatly in- 

 creased. For this reason 1 urge that it would be wise for 



