134 SELECTION ANB USE 



microscopists to construct them for themselves. Where this is 

 desirable, however, the best method of making them is as 

 follows : Select a piece of plate glass, of the thickness of an 

 ordinary slide, and cut it about three inches by one and a quar- 

 ter. Then select another piece of glass, as thick as the trough 

 is to be deep (from front to back) , and cut it to the size of the 

 outside of the trough. From the bottom of this piece of glass 

 cut a strip a quarter of an inch wide, and from the sides also 

 cut strips of the same width. The centre piece may now be 

 thrown aside, and the ends of the bottom strip will make a 

 tight joint with the side strips. The three strips should then be 

 cemented to the large plate, and over them should be cemented 

 a piece of the thin glass used for covers. The strongest cement 

 is marine glue, but it is somewhat difficult to use by those 

 who have had no experience. Prof. Starr, who is well known 

 for his success in keeping and exhibiting living microscopic 

 objects, uses old Canada balsam, and we have seen a large 

 variety of microscopic animals and vegetables which had been 

 kept for months in a healthy condition in such troughs or 



Walmsley's Zoophyte Trough. A serious objection 

 to the troughs which we have just described is the difficulty of 

 cleaning them, and of repairing them when broken. To avoid 

 these difficulties, Mr. Walmsley has devised the little piece of 



Pig. 33. ZOOPHYTE THOUGH. 



apparatus shown in Fig. 33. This trough consists of two glass 

 plates, which are separated by a semi-ring of vulcanized india- 

 rubber, against which they are squeezed so firmly as to be 

 watertight, by means of two vulcanite plates, held together by 

 screws with milled nuts. The front plate may be made of 

 thick or thin glass, as desired, while the depth of fluid em- 



