148 



ACCESSORY APPARATUS. 



we have just detected in a drop of liquid under examination 

 upon an ordinary slip of glass (and covered with thin glass), 

 we transfer this slip to the "growing-slide," fill the cup with 

 distilled water mixed with a small proportion of the water in 

 which the organism was found, and then so arrange the threads 

 (previously moistened with distilled water), that they shall pass 

 from the cup to the edge of the liquid in which the object is con- 

 tained. Thus, as the water evaporates from beneath the thin 

 glass, the threads will afford a continuous supply; and the 

 threads will not become dry, until the whole of the liquid has 

 been absorbed by them and has been dissipated by evaporation. 

 Fresh supplies may, of course, be introduced into the cup from 

 time to time, as may be needed, so as to prevent any loss of 

 liquid from beneath the thin glass ; and in this manner, the most 

 important requisite for the continued growth of aquatic or- 

 ganisms, a constant supply of liquid, without an exclusion of 

 air, may be secured. 1 



68. Aquatic Box or Animalcule Cage. This, also, is an ap- 

 pendage with which every Microscope should be provided, so 

 varied and so constant is its utility. It consists of a short piece of 

 wide brass tube, fixed perpendicularly at one end into a flat plate 

 of brass (Fig. 48) which is perforated by an aperture equal in 



FIG. 48. 



Aquatic Box or Animalcule Cage, as seen in perspective at A, and in section at B. 



diameter to that of the tube, and having its opposite extremity 

 closed by a disk of glass (B b) ; over this fits a cover, formed of 

 a piece of tube just large enough to slide rather stiffly upon that 

 which forms the box, closed at the top by another disk of glass 

 (B a). The cover being taken off, a drop of the liquid to be 

 examined, or any thin object which can be most advantageously 

 looked at in fluid, is placed upon the lower plate ; the cover is 

 then slipped over it, and is pressed down until the drop of liquid 

 be spread out, or the object be flattened, to the degree most con- 

 venient for observation. If the glass disk which forms the lid 

 be cemented or burnished into the brass ring which carries it, a 

 small hole should be left for the escape of air or superfluous 

 fluid ; and this hole may be closed up with a morsel of wax, if 



1 See. the " Micrographic Dictionary," by Dr. Griffith and Mr. Henfrey, Introduction, 

 p. xx. 



