54 SELECTION AND USE 



The instrument, as shown in the cut, is about two-fifths of 

 the real size. When the draw-tube is out, the body has the 

 standard length of ten inches, and it is furnished with the 

 " broad-gauge " screw, to which is fitted an adapter carrying 

 the standard Society screw. 



The first stand placed in market at a moderate price, and em- 

 bodying the special features of the new American model, was 

 the Histological stand of Mr. Zentmayer, which is shown in 

 Plate IV. The base and uprights of this stand are one piece, 

 of a peculiar shape, of great rigidity, to which the bell-metal 

 bar is attached by a joint, allowing the use of the instrument at 

 any angle of inclination ; the perpendicular and horizontal po- 

 sitions are indicated by stops. The coarse adjustment is by a 

 rack and pinion, or in cheaper forms by a sliding tube. 



The fine adjustment is by a concealed lever, acted upon by a 

 delicate screw, and moving the entire body, which is fitted 

 to the grooved bar, giving a steady and delicate movement. 

 The arrangement of the swinging sub-stage and mirrors is 

 easily understood from the engraving. 



The removable sub-stage carries the diaphragms, which can 

 be shifted up close to the object. 



The stage is a modification of the glass stage, and consists of 

 a glass bar kept down by two spring clips, against which the 

 object rests. By this method the object may be moved in the 

 latitude, the longitudinal movement being accomplished by 

 hand. The spring clips may be used independently for hold- 

 ing anything in a fixed position, by simply placing them in the 

 extra holes provided for that purpose. 



The ''Investigator" stand is shown in Plate V, and also 

 presents the special features which we have mentioned. The 

 mirror-bar is swung so that its axis of motion lies in the plane 

 of the object, and it carries the sub-stage, which may thus be 

 inclined to any angle with the plane of the stage, or it may be 

 brought entirely above the latter. The mirror is attached to 

 the mirror-bar by means of a secondary bar, which thus permits 

 the use of the mirror independently of the sub-stage, and both 

 mirror and sub-stage may be moved to and from the object. 

 The sub-stage may be removed entirely when desirable. 



In order to secure the convenience of the low Continental 



