The conditions most favourable to the germination of the spores of the dry rot fungus and to its subsequent growth are (1) a still atmosphere - no draught, (2) a little moisture - not too much, (3) a little warmth, (4) a little ammonia. An air brick on one side of the house is of no use without one on the other side, and both together are useless without holes through the cross walls to allow of a through draught. If the joints of the floorboards are open, a little ventilation may be afforded by currents of air finding their way through. If the upper face of the boards is exposed, the fungus cannot thrive on it; its ravages will be confined to the lower side of the floor, and it will make its way through the boards slowly. Obviously that part of the floor which is covered with loose-textured carpet has the better chance of holding out, but that which is covered with oilcloth, and thus cut off above and beneath from all supplies of fresh air, has everything against it. As regards the moisture, the fungus is greedy for this, although it has to take its supply in very minute quantities from the air or from objects with which it is in contact.

So much moisture, indeed, does it succeed in taking in that it has to discharge an excess, which hangs on its surface in clear sparkling drops, hence its name, Meruleus lachrymans (lachrymans being the Latin for weeping). The remedy is to remove the whole of the floorboards, joists, and other timbers. Every vestige of fungus in any form should be scraped or brushed off the brick or plaster work. Examine the skirting, and remove any that has any suspicion of the growth on it, even the white mould. Clear the ground and take off an inch or two of its surface to ensure getting rid of every trace of the disease and its spores. In some cases an application of fresh limewash to the surface of the walls has prevented further development. Vitriol has also been applied with good effect. If not too expensive, cover the ground with hot lime concrete. Break holes through the cross wall, preferably at the ends, as the air is apt to become stagnant in the corners. Put at least one air brick at the back of the house, and above all things see that the new timber used is not infested with incipient dry rot before it is used.