THE MICROSCOPE AND ITS PARTS. 



Fig. 3. A Growing-slide. 



not more than three-quarters of an inch from the cell, 

 to keep it always full of water, and to have the doubled 

 thread applied closely 

 against the cover. If 

 the water supply is 

 too great, and the cell 

 is disposed to over- 

 flow, shorten the end 

 of the thread against 

 the cover ; if not enough, lengthen it, and do not allow 

 the thread to touch the slide in its course from the 

 reservoir to the cell. 



Again, the observer frequently wants to make a grow- 

 ing-cell of the slide on which he may accidentally have 

 placed a desirable or beautiful object ; that is, he desires 

 to preserve the specimen for several days in the cell 

 without disturbing it, and so taking the risk of losing 

 the invisible thing. He may also wish to watch its 

 growth and development. A reservoir for 'a water sup- 

 ply is necessary ; an " individual " butter-dish makes a 

 good one. Place the slide across the dish, apply a dou- 

 bled thread of sewing-cotton along one side of the square 

 cover, so that each end shall hang down into the dish, 

 and fill the latter with water, which will then pass up 

 and along the thread, and keep the cell full for as long 

 as may be desired. The only objection to this little af- 

 fair is that, after a few days' use, the salts in the water 

 will crystallize on the cover, and so cut off part of the 

 oxygen supply. But no growing-cell is free from some 



