THE "LIVE Box." Many of the larger water animal cuim form interesting subjects while they are alive, because they are quite transparent and the working of the different organs can thus be seen ; they must be enclosed in such a way that they cannot move, and this is effected by placing them, along with a drop of water, in a " live box." The live box (Fig. 724) consists of a plate of brass with a brass ring fixed in the centre, the ring being covered with a glass circle ; another ring covered with a thin glass circle slides upon this, and is pushed clown until the aninialcula is held tightly. This form of live box cannot be used for high powers, because the latter cannot be brought sufficiently near to focus properly. The Housselet's live box, however, enables high matter to get the object required into the field of view, and a good deal of time will he saved by examining first with the microscope alone, using a low power, and moving the slide until the object is directly in the centre of the field of view. The microscope may now be connected up with the camera, and a proper focus being obtained on the ground glass screen, the object will then appear in view ; this will be the case oven if the low power lens is replaced by a higher one before focussing on the screen, only a slight adjustment being required to bring it into the centre of the field. The position of an object
on a permanently mounted slide may be at once located by fixing a small cone of gummed paper in such a position that the object is close to the tip of the cone ; when the slide is placed on the stage of the microscope it is moved until the tip of the cone just passes out of the field of view, and the object is then at once dis covered (Fig. 726). The Maltwood's " finder " is, however, the recognised ap paratus for marking the position of an object for reference. The finder consists of a 3-in. x 1-in. glass slip on which are photographed a number of very small squares ; each of these squares has two powers to be used ; it is larger than the ordinary form, and somewhat differently constructed (Fig. 725). Troughs (Fig. 685) are also used for examining water animalcule under low powers ; they are readily constructed by cementing together three pieces of glass, 3 in. x 1-1, in., with marine glue ; the middle piece of glass, having a half circle cut out of it, forms the trough, while the other two form the sides.