XXV111 



INTRODUCTION. 



and rests on a plate of glass, to which it is fitted air-tight with oil. The inner surface of the 

 cylinder is partly coated with filter paper moistened with water, so that the air in the enclosed 

 space is always kept saturated with watery vapour. To close the space all that is required 

 is to tie a layer or two of sheet caoutchouc over the lower end of the tube of the microscope, 

 and the upper end of the glass cylinder. The object to be examined is placed on the floor 

 of this chamber, and may be examined either with or without a cover-glass. 



Simple moist chamber. A very simple chamber may be made by fixing a ring of glass, a 

 quarter of an inch in height and seven-eighths of an inch in diameter, to an ordinary slide by 

 means of dammar solution. A drop of water is placed in the chamber, which is then covered 

 with a cover-glass, on which the fluid to be examined is placed. The cover-glass is so applied 

 that the drop of fluid hangs into the chamber, as is shown in fig. 14. 



METHODS OF APPLYING HEAT TO MICROSCOPIC OBJECTS. 



Various forms of warm stages are in use ; Max Schultze was the first to use them. 



Simple form of -warm stage. This consists of a thin sheet of copper, three inches long and 

 one and a half inches broad (fig. 12). In the centre is a hole half an inch in diameter. From 

 one side of the plate a narrow copper arm, five inches in length, projects. This is placed on 

 the stage of the microscope, and on it is placed the preparation to be observed. If it be blood 

 (p. 4), the cover-glass must be sealed round with oil to prevent evaporation, and the whole 

 is fixed by the clips on the microscope. Heat is applied to the brass arm by means of a 



Fig. 12. SIMPLE WARM STAGE. 

 Half Natural Size. 



Fig. 13. WARM STAGE AND APPARATUS FOR MAINTAINING A CONSTANT 

 TEMPERATURE UNDER THE MICROSCOPE (Schafer). 



spirit-lamp, and, in order that it may not be over-heated, a piece of a mixture of cocoa- 

 butter and white wax is placed on the copper plate near the preparation. This mixture is 

 so made as to melt at a temperature of 30 C. When it melts the source of the heat must 

 be removed. This does very well for the purposes of the student ; anyone can make it for 

 himself from sheet copper. For accurate experiments it is necessary to have a thermometer, 

 so that the degree of heat can be accurately measured. Such an arrangement is found in 

 Strieker's warm stage. 



