8o 



appliances for Counting. 



Cross-line Micrometers are usually employed for counting small objects, 

 such as blood-corpuscles, yeast-cells, bacteria, etc. 



No. 140. Ocular Cross-line Micrometer. We supply this micrometer 

 to rest on the diaphragm of the ocular or, preferably, for use with a micrometer 

 ocular having an adjustable eye-lens. The division embraces a square of f> mm. 

 divided into squares of 1.0 or 0.5 mm, as may be desired. 



When ordering please state whether the "micrometer scale is required for 

 an ordinary or for a micrometer ocular. 



Xo. 141. P. EHRLICH'S Ocular-diaphragms may be used for counting 

 the number of corpuscles within a field of known area, in a similar manner as the 

 ocular cross-line micrometers. These diaphragms are provided with square openings 

 and are supplied in assorted sets having squares of 1, 2, 3, 4, 6, 8 and 10 mm. 



In the case of ocular cross-line micrometers as well as EHRLICH's diaphragms 



- unless the latter are merely intended for verification of the quantities within 



the same area -- it is necessary for each combination of objective and ocular to 



ascertain, by means of stage micrometers, the actual surface values corresponding 



to the various fields. 



EHRLICH'S diaphragms being primarily designed for use in conjunction 

 with micrometer oculars (see p. 76), it should be expressly stated when ordering 

 them if they are to be used with other types of oculars. 



No. 142. CrOSS-line Stage Micrometers are, as a rule, supplied only in 

 connection with the appliance known as the *Counting Chamber. This latter 

 consists of a cell of exact and uniform depth of 0.1 mm, the bottom of which is 

 ruled in squares. The most commonly used form of such chamber (THOMA's) 

 No. 142 -- contains 400 squares, each having an area of Y^o square millimetre. 



Two cover-glasses, plane-polished, of 0.4 mm and 0.6 mm, accompany each 

 counting chamber. 



