XX 



INTRODUCTION. 



of two leaves, so separated as to allow an evenly enclosed space 

 to exist between them. Then, at opposite points of the space, 

 two small tubes are inserted (a, fig. ix.) To one of these an 

 india-rubber tube 6 is attached, which leads to the vessel for 

 generating steam F. This consists of a flask, through the cork of 

 which a rectangularly bent glass tube is transmitted. The free 

 end of this tube must now be brought into connection with the 

 slide ; in this communication a T-shaped tube is again intro- 

 duced. A lamp with a small flame is placed beneath the flask, 



Fig. VITI. 



ZD 



Metal slide for the conduction of water and steam, a a, conducting 

 tubes ; t, thermometer. 



which is half filled with water, so as to keep up gentle ebullition. 

 The steam escapes through the perpendicular limb of the 

 T-shaped tube, because it here meets with the least resistance. 

 When, however, this is prevented, which is easily accomplished 

 by means of a caoutchouc tube and a clip, the steam passes 

 through the slide, and heats it. If the lamp is now removed, 

 the cooling flask exerts a suction power on the vapour in the 

 space between the two leaves of the slide, and atmospheric air 

 consequently enters ; or if a receiver containing iced water be 

 already prepared, this also may be sucked up, and rapid cooling 

 effected. The temperature is ascertained by the thermometer, 

 which occupies the position shown in the figure. 



Electricity is also an agent of considerable importance in 

 microscopical investigations. Briicke, in his physiological 

 inquiry into the tissues, employed a slide covered with tin- 

 foil, as shown in fig. x. The slide s s was placed on two 



