OF MICROSCOPIC OBJECTS, ’ 29 
tubes into that which embraces. the glass ring and the end 
of the microscope tube—one for the entrance, the other for 
the exit of the gas. This is a simpler and less costly plan 
than that devised by Stricker. Frey observes that it is 
most advantageous to use wnmersion lenses and the moist 
chamber with the hot stage. 
