74 
field of the microscope. — A sliding piece which is actuated 
by a micrometer-screw carries a rotating disc with divided circle ; 
the divisions of the drum indicate 0,002 mm ; complete rotations 
are counted by an index ; the screw measures up to 10 mm. — The 
instrument is arranged to fix on the stages of the larger stands ; 
in the case of those fitted with rotation disc, the latter has to be 
removed. (Fig. 33.) 
When ordering please to state the breadth of the stage 
which it is intended for. 
B. Apparatus for counting. 
CrOSSed-line Micrometer, for dropping into the eye-pieces 
(in particular the micrometer eye -pieces). A square of 
5 mm, divided into squares of 1.0 or 0.5mm, as required; for 
counting scattered particles in the field ; in bone capsule . . . 
Set of Stops of different diameters (1 to 10 mm) for dropping 
into the eye-pieces — micrometer eye-piece preferably — after 
P. Ehrlich 
1) For determining the numerical ratio of the various white 
corpuscles in leucaemic blood. 
2) Tor determining the relative proportions of red and white 
corpuscles in cases of anaemia etc. 
3) The smallest diaphragms for demonstrating objects 
placed in the centre of the field and also 
4) Tor increasing the definition of very fine structural images. 
Crdssed-line Stage Micrometer, a cross-line micrometer, 
being a sq. mm divided into 400 squares, which forms the bottom 
of a cell having an exact depth of 0.100 mm; the cubic contents 
of the fluid resting on one square below the cover-glass are, 
therefore, ^/4ooo cubic millimeters. With 2 plane cover-glasses. 
In case 
