The balsam used as cement between two photographic or other lenses sometimes assumes a sort of fungoid appearance. This, if slight, will practically make no difference to the working of the lens, but it may be removed as follows. Take the lens from its mount (and this removal may necessitate the turning up of the edge of the mount), and place it on a few thicknesses of blotting-paper in a beaker or saucepan. Pour warm water over the lens and keep warm for a time; this will soften tin- balsam, and the lenses may then be carefully slid apart. Note the positions of the lenses, so that in putting them together again the same sidesof the lenses as before may face each other. Clean the lenses with benzole. Now place a lens, concave surface up, on a warm plate, and drop into it a spot of balsam free from bubbles, and lower upon it the convex surface of the other lens, and gently but firmly press well together till the excess oozes out. Put in a clamp or bind up together until dry. On heating, the balsam should remain hard.

On resetting the lens, the fungi id appearance will most likely have disappeared.