122 



SUMMAEY OF CUERENT EESEAKCHES RELATING TO 



purposes, admits of tLe use of very thin cover-glasses, • 005 or • 004 in., 

 and when the cell is screwed up an 1/8 in., 1/10 in., or even 1/12 iu. 

 might be used if required. 



3. The water supply is perfectly under control, and as there is 

 at the same time no filtering action, the object can be supplied with 

 water containing anything necessary to the life of the object. 



4. The current is not interfered with by reducing the depth of 

 the cell. 



5. Objects can be easily put in, taken out, or manipulated in any 

 way by stopping the supply and sliding the glass cover (which by 

 preference should be square) downwards till the opening is large 

 enough to do what is required. To replace the cover, slide it up till 

 there is the least possible opening left and then fill up any air-space 

 in the cell with water from a fine syringe before pushing it quite over 

 the edge. If the under side of the cover-glass be slightly greased at 

 the corners there will be no risk of it floating off. 



This slide is manufactured by Messrs. Swift and Son, and can be 

 made of varying depth and diameter to suit special purposes." 



Stokes's Growing-cell.* — Dr. A. C. Stokes cements to a slide a 

 disk and two rings made from cover-glass,']' the rings having a small 

 piece broken away from each and arranged as shown in fig. 



To use, place on the central disk a small drop of the water con- 



FiG. 23. 



taining the organisms to be kept alive, and over it arrange a large 

 square cover, taking pains to prevent the water from overflowing into 

 the inner annular space. With a camel's hair pencil carefully, and in 

 small quantities, add fresh water at the top or side of the square, 

 until the space covered by the latter and bounded by the outer ring 

 is filled. It will be found that this water will flow between the 

 square and the upper surface of the exterior ring, will enter through the 

 break in the latter, partially filling the outer annular space, and by 

 capillary attraction will occupy a part of the vacancy between the 

 cover and the interior ring, as shown by the diagonal lines in fig. 23, 

 but unless too much water is used, or is supplied in too great quantities 

 at a time, it will not pass the opening in the inner ring, thus leaving 



* Sci.-Gossip, 1884, pp. 8-9 (1 fig.). 



t These can be punched out by the method described by Dr. Beale, ' How to 

 Work with the Microscope,' 5th ed., 1880, p. 73. 



