348 The Microscope. 



of the eye), the image falls in front of the retina. The shadow 

 figure originates in the prolongation of the rays diverging from 

 the image, which is really inverted, but is perceived erect. 



WAYS • 

 AND/AEANS 



Method of preparing dry microscopic plants for the micro- 

 scope. — G. Lagerheim* has found the following method conveni- 

 ent for examination of the Algae or of other plants that have 

 already been dried. 



A fluid is prepared of the following composition : 1 part 

 fused potassium hydrate is dissolved in 5 parts water, and 

 when the solution is complete 5.5 parts are added of glycerine 

 to the consistency of a syrup. The dried Desmids, (Edogoni- 

 acese, or other Algse, are treated with water until they are 

 thoroughly moist ; a small piece of the material is then taken 

 with fine forceps and placed upon the glass slide. One or two 

 drops of the fluid are added, and the Algse distributed as evenly 

 as possible with dissecting needles. The slide is then warmed 

 for a time over a spirit lamp and a cover glass finally placed on. 

 The potassium hydrate has now caused the previously shrunken 

 Algffi to swell and to resume their original form. The addition 

 of glycerine gives consistency to the fluid, so that the Algae 

 can easily be turned over by shifting the cover class, aijid thus 

 observed on different sides, a point of great importance, for ex- 

 ample, in the study of the Desmid?. 



The Algae prepared in this way can readily be drawn or 

 measured. The cover glass is carefull}'^ removed, and, if a low 

 power or a dissecting microscope is used, the object is taken up 

 with a needle or stiff bristle, and again at once placed in potas- 

 sium acetate or glycerine. If, on the contrary, the whole mate- 

 rial thus prepared has to be got ready for drawing or measuring, 

 a drop of acetic acid is added after removing the cover glass. 

 The Algae are in this way embedded in potassium acetate and 



*Bot. Centralbi. — Cf. J. R. Micros. Soc. 



