ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 



311 



Fig. 71. 



Fig. 72. 



which the slide (fig. 71) with the object can be placed. Above and below 

 this are other vertical openings c and d, communicating with it, the 

 upper one d receiving the objective, and the lower one c a diaphragm of 

 glass. To prevent cooling, the space between the objective and the sides 

 of the upper opening can be stopped 

 with cotton wool. A thermometer t is 

 inserted in a tube at one side of the 

 apparatus, as shown in both figures. 



It is essential, in order to insure the 

 same temperature of the water in the 

 reservoir and stage, which communi- 

 cate by the circulating tubes a a and 



b b', that the stage should be above the level of the water in the vessel, 

 and therefore that the Microscope itself should be elevated as shown in 

 fig. 52. 



Professor Eanvier describes the great advantage of the apparatus to 

 consist in the fact that a constant 

 temperature can be readily main- 

 tained for several hours. When the 

 temperature of the water has been 

 raised to 40° C, an observation can 

 be continued for a quarter of an 

 hour without any reheating, as the 

 cooling proceeds so very slowly. 

 The preparation is at the very centre 

 of the stage, and the aperture below 

 being closed by a glass diaphragm 

 and that above by cotton-wool, the 

 object is protected against all the 

 usual causes of cooling, and its tem- 

 perature is very nearly that indicated 

 by the thermometer.* 



: Dr. M. Flesch | suggests a form 

 of stage available for both high and 

 low temperatures, and especially for 

 rapid changes of temperature, also 

 allowing the Abbe condenser to be 

 used for illumination as well as the 

 ordinary polarizing apparatus. 



The author discusses some of the 

 preceding stages, condemning Max 

 Schultze's. He considers Eanvier's 

 to come the nearest to fulfilling the 

 conditions which he laid down for 

 himself. Hartley's J and Symons' § 

 he considers to each present im- 

 portant advantages; the former dues not, however, allow the temperature 

 to be determined with exactness ; the latter he fears would not admit of 

 very rapid changes, and the cover-glass on which the object is placed 

 would be liable to be broken or displaced by quick cooling. 



The stage (fig. 72) is a shallow box, into which pass the tube a for 



* To prevent the cooling of tlie object by the objective, especially when the focus 

 is shurt, it has been suggested to place an ivory tube 30 mm. long over the objective. 

 Dippel, torn, cit., 1882, p. 655. f Zeitschr. f Wiss. Mikr., i. (1884) pp. 33-8 (1 fig.). 



t See this Journal, 1881, p. 672. § See this Journal, 1882, p. 21. 



