ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



825 



indlarubber ring into tte box. For use as a growing slide a ring of 

 indiarubber or of gutta-percha tissue is placed as before in the bottom of 

 the box (but in this case the cut in the ring is to be placed as indicated 

 by the dotted lines in Fig. 186) ; 

 the object to be examined is 

 placed within the ring, and 

 water added through the slot 

 F, which passes into the box 

 outside the indiarubber ring. 

 Water may also be added to 

 supply the loss from evapo- 

 ration from time to time, 

 through the slot F in the ring 

 B, which slot may be closed 

 by a plug of cotton wool, to exclude dust and prevent evaporation. 

 When it is desired to use the apparatus as a live-box, the india- 

 rubber ring may be dispensed with. The object is placed in the ring 

 B, the cover D pushed in as far as found desirable, and water added 

 if required by the opening or slot F, which may be closed by a plug 

 of cotton wool as before. 



The advantages of the apparatus are that it admits of the easy 

 arrangement of the object to be examined ■ that it is readily cleaned ; 

 that as no metal is used in its construction, it allows of prolonged 

 observations being carried on without disturbance of the object ; that 

 water, either fresh or salt, may be added from time to time ; and that 

 the thin cover-glass permits of high powers being used, and is readily- 

 replaced when broken. 



Malassez's Moist Chamber.* — Professor Malassez recommends a 

 graduated moist air chamber. A thick slide has in its upper surface 

 a circular groove 1*5 mm. broad, 1 mm. deep, and 7*5 mm. in 

 internal diameter. It is pierced outside the groove by three or four 

 holes into which are introduced fine screws ; the heads are on the side 

 furthest from the observer (but do not project beyond the lower side 

 of the slide). The points are directed upwards and project so that 

 the cover-glass can be laid upon them ; the preparation which is 

 to be examined is placed on that part of the slide which is sur- 

 rounded by the groove, and by putting some water on the edge of 

 the cover-glass, an air-tight space is obtained without the risk of the 

 water coming into contact with the object, as the groove prevents its 

 passing inwards. By removing the screws any required depth can be 

 given to the space within the chamber, with the aid of a pointer for 

 measuring the depth. By this means the chamber may be utilised for 

 counting (e. g. blood-corpuscles) by given units of space, by having a set 

 of ruled micrometer spaces either on the stage or in the eye-piece. 



Mackenzie's Swinging- Substage. — We briefly alluded, on p. 515, 

 to a simple form of substage devised by Mr. J. Mackenzie, and 



Gaz. Med., 1879, p. 632. Cf. Zool. Jahresber., i. (1880) p. 25. 



