The Mickoscope. 131 



If it is desired to convert this or any other slide of the kind into 

 a growing-cell, it is done by the well-known method of placing the 

 slip across a small saucerful of water, with a doubled and twisted 

 thread of sewing-cotton in close apposition with the edge of the 

 cover, both ends of the thread hanging freely in the water. The 

 latter will, flow up and supply that lost by evaporation, provided the 

 water is always in contact with the lower surface of the slide. This 

 " dodge" is successful for a few days, but it always ends badly, as 

 the salts in the water will crystallize at the cover margins and cut off 

 the oxygen supply. 



It often happens that the conditions and the environment are 

 such that an immense number of minute Infusoria, all belonging to 

 the same species, are suddenly developed in the aquarium, infusion 

 or maceration, and it becomes interesting to isolate a few to study 

 their life-history. Such an advent of Monads, Heteromit?e and 

 other similarly minute creatures is not rare. For the study of 

 such truly microscopic objects the writer devised a simple life-slide, , 

 describing and figuring it in Science Gossip for January, 1884,' 

 from which paper I shall quote without using inverted commas. 

 To make this, cement with Canada balsam in the center of a slip 

 a thin circle \ inch or less in diameter ; use a y^ inch circle if pos- 

 sible. In the latter case then take a glass or zinc or other kind of 

 ring with a quarter-inch aperture, break a small piece from one 

 side, and fasten this broken circular band about the central disc. 

 From another ring with a f inch or larger aperture break a piece as 

 before, and cement this broken band around the inner ring so that 

 its broken part shall be opposite the unbroken curve of the latter, 

 and, with a thin, square cover, the cell is complete, the depth de- 

 pending upon the difference in the thickness of the rings and the 

 central circle. 



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

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

 square cover, taking care to prevent the water fi-om overflowing into 

 the inner, annular space. With the camel's hair brush carefully, and 

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

 never at the bottom or near the opening in the outer ring. It will 

 be found that the 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 the diagram. 

 Fig. 2,] but unless too much water is used or is supplied in too 



