1895 THE MICROSCOPE. 29 



solution dropped over them. When it is desired to obtain a 

 large number of the organisms, they may be killed in a vessel 

 and then a stronger solution must be used. In the vessel, the 

 animals will fall to the bottom ; the water should be drawn off 

 above them. Then add seventy per cent alcohol and replace 

 this with alcohol slightly acidified with hydrochloric acid. 

 This latter solution should be run over the animals fixed 

 upon a slide. The effect of the latter solution is to remove all 

 trace of the iron salt. This should be immediately drawn off 

 and pure alcohol added. The animals can then be mounted in 

 glycerine. 



Mounting Hydra. — Hydra viridis is nearly always to be 

 found on the under surface of the leaves of Lemna. It is also 

 found adhering to other plants. For an acceptable mount it 

 should be prepared so as to exhibit its expanded tentacles. 

 The folh^wing is a method by which this may be accomplished. 

 Have a slide with a well dried cell of sufficient depth ; drop the 

 hydra on the end of a plain glass slip. Hold the slip near the 

 top of the chimney of the student lamp. You can see then if 

 its tentacles are expanded. If they are, quickly hold the slip 

 with the hydra over the chimney end about an inch above it. 

 Hold it there from three to five seconds ; then quickly place the 

 slip upon a cool, heat-conducting surface. When cold transfer 

 the animals to the prepared cell and mount in glycerine. All 

 kinds of hydra and many other of the larger zoophytes may be 

 fixed and mounted in this manner. 



How to Examine Coal.— Coal is of vegetable origin. To 

 examine its structure it is necessary to have very thin sections. 

 To obtain such sections, macerate the coal for about a week in 

 a solution of carbonate of potassium when thin slices may be 

 cut with a razor or a microtome. These sections should be 

 gently heated in nitric acid, and when they turn yellow, should 

 be washed in cold water and mounted in glycerine. Spirit or 

 balsam will render the sections opaque. 



SCIENCE-GOSSIP 



Drinking Cups and Diphtheria. — Dr. Chas. H. Stowell, 

 formerly Editor of The Microscope says of Washington Schools; 



