42 



THE MICROSCOPIST. 



tube for the entrance of gas, while the other serves for 

 its exit. 



For the study of phenomena in the fluids, etc., of warm- 

 blooded animals, we need, in addition to the moist cham- 

 ber, some way of keeping the object warm. This may be 

 roughly done by a perforated tin or brass plate on the 

 stage, one end of which is warmed by a spirit-lamp. A 

 piece of cocoa butter or wax will show by its melting 

 when the heat is sufficient. Schultze's warm stage is a 

 more satisfactory and scientific instrument. It is a brass 

 plate to fit on the stage, perforated for illumination, and 

 connected with a spirit-lamp and thermometer, so that 



FIG. 21. 



Strieker's Gas Chamber. 



the amount of heat may be exactly regulated. Other 

 arrangements have been proposed to admit a current of 

 warm water, or for the passage of electricity through an 

 object while under observation, which are scarcely neces- 

 sary to describe. 



The Polariscope. The nature and properties of polarized 

 light belong rather to a treatise on optics or natural phi- 

 losophy than to a work like the present, yet a very brief 

 account may not be out of place. We premise, then, that 

 every ray or beam of common light is supposed to have 

 at least two sets of vibrations, vertical and horizontal. 

 As these vibrations have different properties, the ray when 



