68 YELLOW FEVER AT LISBON. 



these germs become inactive; and this view receives 

 considerable support from the well-known fact that the 

 mortality due to this disease always largely diminishes 

 upon the occurrence of sudden and well-marked atmo- 

 spheric disturbances such as heavy rains, storms, or a 

 fall in the temperature. But wherever there are popu- 

 lous sea-ports or other towns in low-lying situations 

 as long as the summer temperature keeps up sufficiently 

 high (even though it be for a single season of excep- 

 tional heat) we may on the other hand pretty safely 

 assert that the place is never secure from the possible 

 inroads of this terrible pestilence. 



We may quote, for instance, the case (amongst 

 others) of the fearful outbreak of epidemic yellow 

 fever at Lisbon, at the close of a very hot summer, 

 in October and November 1859, which attacked nearly 

 1 9,000 people, and carried off some 6,000 of the population 

 living in and around the city, many of them being 

 persons of the upper classes. On the whole, this is 

 the most disastrous epidemic of this fell disease which 

 has visited Europe during the century. 



We have dwelt somewhat at length upon this subject, 

 because yellow fever forms a constant bugbear to all 

 European travellers and residents, throughout tropical 

 America, while the range of this malady seems to be 

 peculiarly one dependent upon such questions of 

 elevation and temperature as we have just been con- 

 sidering. And the rule that holds good in Mexico 

 seems generally to maintain itself under similar con- 

 ditions elsewhere, notwithstanding that some exceptions 

 are alleged to haVe occurred, owing to special circum- 

 stances, in Peru and elsewhere in South America. 

 All that we shall venture to say on this head is that 



