BIOLOGICAL PAPERS. 147 



the eye and any strong light. The upward movement of the red 

 liquid began at once and continued until the veins were colored 

 to their tips at the apex of the leaf. 



In the second method of demonstration by projecting the pre- 

 pared leaf on a screen a special glass and metal cell was used. 

 This cell is so constructed that it does not interfere with the nor- 

 mal activity in the loaf, but keeps the leaf flattened under the 

 objective, prevents the upward flow of the eosin solution on the 

 surface of the leaf next to the glass, and permits any necessary 

 movements for accurate adjustments on the stage of the projec- 

 tion microscope. As a large field and low magnification are 

 desirable conditions in this demonstration, a regular lantern slide 

 projection apparatus was used as a low power projection micro- 

 scope.^ A vertical glass plate Avas attached to the slide stage 

 which was then moved away from the condenser lenses a few 

 inches and the lamp was so adjusted that the light was focused on 

 the vertical glass plate. The quarter size projection lens was 

 moved to such a point that it projected on the screen a clear pic- 

 ture of an object held against the vertical glass plate which was, in 

 effect, the stage of the projection microscope. A cooling tank of 

 distilled water was placed between the condenser lenses and the 

 glass stage to prevent undue heating of the leaf. A drop or two 

 of water was then put into the special cell. A barley leaf, cut as 

 described above, was placed in it. the cell placed on the glass 

 plate and the transparent veins of the leaf sharply focused on the 

 screen. The normal colors of the leaf having been seen, a few 

 drops of strong eosin solution were added to the water in the 

 cell and the movement of the colored liquid along the veins was 

 immediately visible as far as to the rear of the room or forty 

 feet from the screen. 



^Cole's Manual of Biological Projection and Anasthesia of Animals, p. 38. 



