ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



673 



supports for the tube a a and as stops for the slide, and which may- 

 be cemented to the stage by mucilage, to make the apparatus more 

 steady. These corks can be replaced by strips of sheet tin or brass, 

 so bent as to serve the same pui-pose. The tube a a is placed in the 

 usual position of the slide upon the stage, and the slide is placed 



Fig. 15i. 



upon it ; the light passes between the two limbs of the tube. The 

 vessel B receives the water discharged at c. As long as the water 

 in A is kept at 100° C, and a constant relation is maintained between 

 the height of the water in this vessel and the stage, the temperature 

 of the slide will remain constant as long as the water flows. By 

 raising or lowering A, the velocity of the current of water may 

 be increased or diminished, and the temperature of the slide is 

 controlled. 



By a somewhat rough measurement of the temperature obtained 

 with this apparatus, Professor Bartley finds it possible to procure a 

 range of about 45° C, or from 27° C. to 70° C. As the normal tem- 

 perature of the human body is 37° C, it will be seen that the range 

 is all that is needed for the object for which it was intended. The 

 higher temperatures are convenient for favouring chemical reactions 

 under the Microscope, or for the evaporation of liquids, or other uses 

 where a gentle heat and uniform temperature are desired. 



Hume's Frog-plate. — Mr. A. Hume has devised the apparatus 

 shown in Fig. 155,* for the greater convenience of the frog while 

 under examination. To a plate of tlie ordinary form is attached 

 (sliding in gi'ooves) a brass box without a bottom, and pierced with 

 apertures, in which the frog is placed, and in which it can freely 



* See this Journal, iii. (18S0) p. 174. 



