100 LIMITATION. 



produce the cause of it for itself, and if the conditions of 

 growth are not present, then will the spot be exempt, even 

 if very near to the most poisonous places. Thus may we, 

 and only thus, explain the occurrence of agues, yellow 

 fever, and cholera, on only one side of a house, or one 

 end of a room, or one si(^ of a street, or wall, or road. 

 A wind may indeed waft the spores in small quantity to a 

 distance, but unless there are there the conditions essen- 

 tial to an adequate reproduction, the spores must lie dor- 

 mant and harmless. For such reproduction, the marsh 

 mist may be one of the most important elements, but that 

 alone will not suffice, since we know that the disease is 

 not proportional to its frequency or intensity. Other and 

 very local conditions seem to exercise a peculiar power. 

 Thus a new house is known to resist disease better than 

 an old one, and a residence protected by an annual culti- 

 vation, immediately around it, is more safe than one which 

 is encircled by lawns in grass. During some unusually 

 sickly years, when scarcely an inhabitant of the skirts of 

 the city escaped marsh fever, the wind set, often for a 

 long period, directly from the infected regions into the 

 heart of the city. In perhaps half a minute from the 

 time when the south-western air left the meadows and 

 pestilential borders of the town, it had crept into every 

 chamber of the place; yet physicians here, well know that 

 no disease of a malarious character invaded these cham- 

 bers, which were, most of them, left open during every 

 night of the sultry autumn. 



Writers entitled to credit and authority, by position 

 and professional character, assert, that a gauze veil, or a 

 gauze screen in a window, adds much to the security of 

 the wearer or the occupant of a chamber, in even the most 

 unsound places. We can scarcely see how any gas or 



