PRACTICAL HISTOLOGY. 



INTRODUCTORY. 



THE practical study of Histology is mainly depen- 

 dent upon the use of the microscope. The microscope 

 is a combination of lenses arranged for the purpose 

 of obtaining and viewing a magnified image of any 

 minute object. The lenses are set in a tube of vari- 

 able length the tube of the microscope (Fig. 1, , t') 

 and this is itself supported in a vertical position, on 

 a firm, metal stand, which is provided with an 

 arrangement by which the tube is capable of being 

 moved, without lateral deviation, in a perfectly 

 straight, up and down direction. This arrange- 

 ment is termed the adjustment. Its purpose is to 

 bring the microscope into that position with regard 

 to the object in which the latter is most clearly 

 seen. The object is then said to be in focus. 



Two adjustments are commonly provided: one 

 the coarse adjustment (adj) serves to bring the lenses 

 roughly into the focal position, and is either a tele- 

 scopic joint or a rack and pinion movement; the 

 other the fine adjustment (adj f ] is a fine screw, and 

 by its means the focus may be obtained with com- 

 plete exactness even when the highest magnifying 

 powers are employed. The stand is further pro- 

 vided with a 'rigidly connected, horizontal table or 

 stage (st), upon which the object is placed, and which 

 projects below the tube and is provided with a cir- 

 cular aperture to admit light from below to the 

 object, capable of being varied by means of a dia- 

 phragm (d) furnished with holes of different sizes. 

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