234 MOUNTING OF OBJECTS. 



employed, and comparing the specimens from time to time, so 

 as to judge how each is affected. 



132. Of Mounting Objects in Fluid. As a general rule, it is 

 desirable that objects which are to be mounted in fluid, should 

 be soaked in the particular fluid to be employed, for some little 

 time before mounting; since, if this precaution be not taken, 

 air- bubbles are very apt to present themselves. It is sometimes 

 necessary, in order to secure the displacement of air contained 

 in the specimen, to employ the air-pump in the mode already 

 directed ( 128) ; but it will sometimes be found sufficient to im- 

 merse the specimen for a few minutes in alcohol (provided that 

 this does not do any detriment to its tissues), which will often 

 penetrate where water will not make its way; and when the 

 spirit has driven out the air, the specimen may be removed back 

 to water, which will gradually displace the spirit. "When Deane's 

 Gelatine is used, however, all that can be done, will be to drain 

 the object of its superfluous water before applying the liquefied 

 medium ; but as air-bubbles are extremely apt to arise, they must 

 be removed by means of the air-pump, the gelatine being kept 

 in a liquid state by the use of a vessel of hot water, as in the 

 case of Canada balsam. In dealing with the small quantities of 

 fluid required in mounting microscopic objects, it is essential for 

 the operator to be provided with the means of transferring very 

 small quantities from the vessel containing it, to the slide, as 

 well as of taking up from the slide what may be lying superfluous 

 upon it. The straight and curved-pointed "dipping-tubes" (Fig. 

 51, A, B) may be made to answer this purpose ; but it is much 

 better that tubes for this purpose be furnished with a bulb, like 

 that of the Chemist's "pipette," and that their orifices be drawn 

 to a fine point. The fluid is drawn into the tubes by suction, 

 and expelled by the pressure of the breath ; the curved-pointed 

 tube will generally be the best for introducing fluid beneath the 



flass cover, and the straight-pointed for simply filling cells or 

 >r taking up superfluous fluid. The Author has of late found 

 very great convenience in the use of a small glass syringe, the 

 orifice of which is slightly curved and drawn to a fine capillary 

 point ; for as the syringe works independently of the mouth, its 

 orifice may be applied in any way that may be found convenient; 

 and when the mouth is freed from the efforts of suction and 

 ejection, the eyes can be better employed in watching the opera- 

 tion. Besides the pipettes and the syringe, some blotting-paper, 

 of the most bibulous kind that can be procured, will be found 

 very useful. 



133. There are certain objects of extreme thinness, which re- 

 quire no other provision for mounting them in fluid, than an 

 ordinary glass slide, a thin glass cover, and some gold-size or 

 asphalte ( 120). The object having been laid in its place, and 

 a drop of the fluid laid upon it (care being taken that no air- 

 space remains beneath the under side of the object and the sur- 



