8i = 



Besides the counting chamber No. 142 we supply various other counting 

 chambers as well as accurately calibrated mixing pipettes for diluting blood and 

 the like. 



No. 149. Blood-COUnting Apparatus, consisting of a counting chamber 

 and one or two accurately calibrated mixing pipettes, is likewise supplied in 

 various combinations. THOMA's Haemocytometer, No. 149, supplied with one 

 mixing pipette for red corpuscles and another for the white, is the most frequently 

 used apparatus of this kind. 



Further information regarding the variety of forms of the 

 divisions of squares in our counting chambers, the various classes 

 of mixing pipettes and complete counting apparatus are contained 

 in a separate pamphlet dealing with blood-counting apparatus 

 (M 10), copies of which may be obtained on application. 



Marks Codeword 



THOMA'S llaeinocytomcter (Blood-counting Apparatus), 



No. 142. with '2 mixing pipettes, in case . 



30. Peira.\o 



C. *Apertometer, *Test-plate, * Diffraction Apparatus. 



Nos. 155 and 156. Apertometer. A simple apparatus for determining the 

 numerical and angular aperture of objectives, the Apertometer, was designed 

 by Professor ABBE in 1876. It is adapted for any large or medium stand fitted 

 with a draw-tube. A low-power objective of about 40 mm focal length, which 

 screws into the lower extremity of the draw-tube, is supplied with the instrument, 

 but under appropriate stopping the BERTRAND lens may, with Mineralogical 

 Stand HIM, be used instead. The auxiliary microscope, formed by the combin- 

 ation of the low-power objective with the ocular, being focussed upon the exit 

 pupil of the objective to be examined, the numerical aperture of the latter i may 

 be read off from the apertometer by means of two movable metal indicators. 



Further particulars regarding principles of construction of the apparatus 

 and the method of measuring with it are contained in the Journ. of the R. Micr. 

 Soc. (1), vol. I, 1878, pp. 1922, and (1), vol. Ill, 1880, pp. 2031; E. ABBE, 

 Gesamm. Abhandl. I, 1904, pp. 113118 and pp. 227243; see also DIPPEL, 

 "Das Mikroskop", vol. I, pp. 348352. 



i, cfctta. 



