GLASS TROUGHS AND CELL?. 195 



forms and shapes. Botterill's (fig. 132) consists of 

 two brass plates, screwed together by binding screws, 

 and holding between them two plates of thin glass, 

 and which, are maintained at a proper dis- 

 tance by inserting half of a circular flat disc 

 of india-rubber. 



Beck's glass trough, for chara and polypes, 

 a sectional view of which is shown at fig. 133, 

 is made of three pieces of glass, the bottom 

 being a thick strip, and the front a of 

 thinner glass than the back & ; the whole is 

 cemented together with Jeffery's marine- 

 glue. The method adopted for confining 

 objects near to the front glass varies ac- 

 cording to circumstances. One of the most 

 convenient plans is to place in the trough a 

 piece of glass that will stand across it 



diagonally, as at c ; then if the object be PIG 13 

 heavier than water, it will sink, until stopped 

 by this plate of glass. At other times, when used to 

 view chara, the diagonal plate may be made to press it 

 close to the front by means of thin strips of glass, a 

 wedge of glass or cork, or even a folded spring. 

 When using the trough, the microscope should be 

 placed in a nearly horizontal position. 



Growing. cells. Considerable attention has been given 



FIG. 134. Weber's Slip with Convex FIG. 134a. Seek * Current-slide Live- 

 Cell for use as a Live-trough. cell. 



to various forms of growing-cells for maintaining a con- 

 tinuous supply of fresh water to objects under observa- 

 tion, and for the purpose of sustaining their vital 

 energy for a long period. The employment of live-cells 

 is strongly commended to microscopists, as there is yet 

 much to be discovered concerning the metamorphoses 

 which some of the lower microscopic forms of plant 

 o 2 



