2554 



Journal of Applied Microscopy 



glass over one side of the hollow, Fig. 10, so that the water in the hollow will 

 run in between the cover-glass and slide and the organism will be in the hollow 

 under the cover-glass. Slides may be left in this condition for hours, ready to 

 be closed just before use, if placed under a bell jar in an atmosphere saturated 

 with moisture ; but they are usually closed in at once, for the organisms live for 

 surprisingly long periods in the closed cells. To close the cell and exclude all 

 air bubbles, push the cover-glass over the hollow and, at the same time, add just 

 enough water from a pipette to exclude all air, and then center the cover over 

 the hollow. Press the cover-glass gently, and any excess of water will appear 

 at its edges and must be removed by absorption or with a pipette, as in mount- 

 ing amoebae, etc., on plane slides. When all excess of water has been removed, 

 the cover-glass will adhere to the slide in whatever position it is held, and it is 

 now ready for use on the projection microscope. 



After a time, evaporation at the edges of the cover-glass may cause air to be 

 drawn into the hollow. If it is necessary to remove it, place the slide on a table. 



Fig. 10. — Hollow-ground slide with the hollow a nearly filled with water w con- 

 taining an organism o. The cover-glass c is in its first position with water -v 

 underneath. The cover-glass is to be pushed in the direction of the arrow, 

 while just enough water is being added with a pipette at e to exclude air 

 bubbles from the hollow as the cover-glass is pushed over and made con- 

 centric with it. 



push the cover-glass along until one edge of the hollow is exposed, tilt the slide 

 so that the air bubbles gather at the open edge of the hollow, add enough water 

 with a pipette to expel the air and replace the cover as at first. 



C. Mounting organisms, e. g., colonies of spongit/a, active species of all types, 

 plant specimens, etc., in open top cells. 



The use of this type of cells (Fig. 9, No. 14 and 16-20) is so easy that all 

 necessary directions will be included in descriptions of three interesting experi- 

 ments, the evolution of oxygen by green plants under the action of sunlight or 

 electric arc light, the circulation of water through colonies of spongilla, and the 

 study of larvae and pupte of the mosquito under hypnosis and anesthesia pro- 

 duced by chloretone. 



The demonstration of the evolution of oxygen by green plants is an exceed- 

 ingly instructive and interesting experiment, especially when the different effects 

 produced by varying the degree of heat and the application of cold are shown in 

 succession on the same specimen. Select several vigorous shoots of the common 

 choke-pondweed {Anacharis or Elodea Canadensis), a perennial which grows well 

 in aquaria throughout the year, and cut off the stems with scissors about an inch, 

 or less, if the cell to be used is small, from the apex, being careful not to injure 



