103. =Warm stage= after Stricker. This stage consists of a metal chamber, through which warm water is made to flow when in use, and is provided also with a condenser and thermometer. It may be screwed firmly to any of the square microscope stages =14.--= [Illustration: Stricker's Warm stage No. 103.] 104. =Warm stage= after Errera, permitting rapid changes from low to high temperature and vice-versa. It includes 2 vessels for cold and hot water, mounted on tripods, with rubber-tubing etc. =24.--= =Photo-micrographic Apparatus.= [Illustration: Photo-micrographic Apparatus No. 105.] The method of employing this apparatus and the general technique of photo-micrography are treated of in a separate pamphlet containing also four photo-micrographs taken with this apparatus. This little work is furnished with each apparatus. 105. =The Photo-micrographic Apparatus= consists of a heavy iron foot supporting a stout column in which another iron support moves vertically. This latter holds the camera and may be firmly fixed at any height by means of a thumb-screw. This permits the accurate adjustment of the camera to microscope stands of various sizes. The length of the camera is also adjustable by means of a thumb-screw sliding in the upright support. Regulation of the field of the camera is accomplished by a revolving disc diaphragm with openings of five different sizes situated in the neck of the camera. Two simple plate-holders for plates 9×12 and 13×18 cm are supplied with each camera, as are also a ground glass plate and clear glass plate in the frame of the camera serve to catch the picture in the plane of the photographic plate, and a simple lens aids in obtaining a correct focus of the image. A white glass plate, mounted on a stand is of use in diffusing direct sunlight so as to make it available for photographic purposes, and three discs of yellow, blue and green glass are provided which may be inserted over the iris- diaphragm of the condenser when colored light is required. It is of great advantage to interpose an illuminating lens between the source of light and the mirror, thereby condensing the light-rays, giving a uniform illumination and preventing the heating up of the entire stand, which is a disturbing factor in retaining the focus. The illuminating lens also serves to lessen the time of exposure.