MICROSCOPICAL DIAGNOSIS. 



chaser. It should be so delicate that the slightest movement of the 

 milled head will be apparent by an alteration in the distinctness of 

 the image. 



The Stage "H," the part upon which rests the object to be ex- 

 amined. It is made of either glass, brass, or hard rubber. In order 

 that the stage may be suitable for all kinds of work, it should have 

 combined "the minimum of thinness with the maximum of 

 strength." 



The Object-Carrier "I," attached to the stage in order that the 

 object may be moved more accurately and carefully about. 



Although not strictly necessary, yet it is a great convenience, 

 and as it increases the cost of the instrument but a trifle, it should 

 accompany every stand. 



A "Mechanical Stage" is so arranged that the object can be 

 accurately moved by means of finely adjusted screws. 



The Diaphragm "K." This is placed beneath the stage and has 

 different sized openings to regulate the amount of light. The 

 smaller holes are employed with the higher powers. An "Iris diaph- 

 ragm" is so constructed that the size of the opening may be 

 changed without ceasing to observe. 



The Sub-Stage is used for holding various accessories; as con- 

 densers, polarizing apparatus, etc. A stand should be examined 

 with especial reference to the following four points; (see Carpenter 

 on the Microscope. *6th Ed. p. 47.) 



First. The optical parts and the stage should be so disposed 

 as either to be altogether free from tendency to vibration, or to 

 vibrate together. 



Second. It should be capable of accurate adjustment to every 

 variety of focal distance, without movement of the object. 



Third. It should be capable of being placed in either a verti- 

 cal or a horizontal position, or at any angle with the horizon, with- 

 out deranging the adjustment of its parts to each other, and without 

 placing the eye-piece m such a position as to be inconvenient to the 

 observer. 



Fourth. Simplicity in the construction and adjustment of every 

 part. 



The Mirror "i." It should consist of two surfaces; a plane 

 surface, to reflect the light just as it falls upon it, and a concave 

 surface, to converge the rays. 



