I have deferred describing these protected shelters until now, but as a matter of fact they had been devised and adopted nearly a year previously, though not many of them had got into actual use. The protection consists essentially of a damp blanket fitting closely over the entrance to the cellar or dugout or emplacement, whichever it may happen to be. The value of the blanket depends on the fact that if you prevent the movement of air you prevent the movement of gas. That is all there is to it. Stop any possible draft and you will keep out the gas. In practice the blankets are kept rolled up out of the way and are let down only when the alarm is sounded or when gas is about. In order to get an air-tight joint the blanket is made to rest on a sloping framework set into the entrance to the dugout. To make sure that the blanket really does remain stretched out over the frame and does not gape at all, two or three wooden battens are fastened across it at intervals. Where space is available two such sloping blankets are used, at least two feet apart and preferably far enough apart to allow a stretcher in between. This forms an “air lock”--you must go into the lock and close the outer blanket before going through the inner one--and not only makes protection of the interior doubly sure but makes it possible to enter the dugout even in the middle of an attack or bombardment. In the old days the blankets used to be sprayed with the Vermorel sprayer solution, but anything that will keep them damp and flexible will do. In the early days, too, the companies or batteries used to do all their own work on protecting dugouts, and it was always possible in cold weather to obtain an extra supply of blankets on the plea that they were required for making gas-proof shelters. Nowadays a close eye is kept on these supplies, which are doled out by the engineers, and it is seen that if blanket material is supplied for protected dugouts it is going to be used for protected dugouts, and for nothing else. Gradually all dugouts, cellars and buildings within the gas-shell area--let us say up to three miles from the front line--are being provided with blanket protection, which means a big decrease in casualties, for once inside such shelters men can sleep in more or less comfort until they again have to don their respirators and face their tour of duty in the poisoned air outside.