ZOOLOGY AND BOTANY, MICROSCOPY^ ETC. 



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near the object. The box is painted on the inside with black varnish, 

 and a piece of cardboard moistened with water lies beneath the foot of 

 the Microscope in order to prevent its moving and to keep the air within 

 moist. The focus is easily adjusted to the object by means of the fine- 

 adjustment s which projects above the cover ; two openings in the side, 

 one of which is shown at o, enable the slide bearing the object to be 

 moved, when necessary, by a pair of forceps. It is still more convenient 

 to fix the slide on a wire which goes through a cork fitted to the 

 opening o. 



It is easy by means of this heating apparatus to observe and demonstrate 

 the influence of temperature on protoplasm-currents. To take observations 

 at low temperatures it is sufficient to enlarge the hole Z, in order from 

 time to time to place pieces of ice in the cold water.* 



Maintaining a constant temperature and varying the temperature. — For 

 varying the temperature with rapidity, Prof. Strieker suggested f the arrange- 

 ment shown in fig. 79 (centre of stage omitted). To the tube a, com- 



FiG. 79. 



municating with the stage, is attached an indiarubber tube h, which leada 

 to a flask r for generating steam. The steam escapes through the per- 

 pendicular limb g of the T-shaped tube which is interposed between the 

 flask and &, because it here meets with the least resistance. When this is 

 prevented by means of a caoutchouc tube and a clip, the steam will pass 

 through the slide and heat it. If the lamp is removed, the flask in cooling 

 will act by way of suction on the vapour in the slide and air will enter, 

 or iced water may sucked up through the tube a' and rapid cooling 

 effected. 



A preparation may also be subjected to sudden alterations of tem- 

 perature by the apparatus shown in fig. 69. | A clip is placed on the 

 tube c, leading from the water receptacle by means of which the access of 

 the warm water to the stage may be interrupted. The end of the escape 

 tube d is then allowed to dip into a vessel of cold water. This done, cold 

 water may be readily introduced into the stage so as to cool it suddenly, 

 by suction through the tube c, which must be provided with a branch 

 (not shown in the fig.) between the clip and the stage for the purpose. 

 To effect a sudden rise, all that is necessary is to open the clip. 



An excellent contrivance for maintaining a constant temperature with 

 a hot stage, is that devised by Prof. E. A. Schdfer,% on the model of the 



* Parnim is also stated (Thanhoffer, torn, cit., p. 89) to have adopted the same plan 

 as Sachs of enclosing tlie whole Microscope, but we have not been able to find the 

 reference to his description. t Op- cit., pp. xx.-xxi. 



% Burdon-Sanderson, op. cit., pp. 7-8. § Op. cit., pp. 22-3 (1 fig.). 



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