75. =The Micro-Spectroscope= fits into the tube of the microscope like any ordinary eye-piece and may be fixed in any desired position by means of the thumb-screw M. The position of the bright and dark lines of the spectrum and their respective wave lengths are ascertained by means of a scale. The flat drum A, the interior of which is shown in section, contains the slit and the comparison prism. The slit is regulated by the screws F and H. The lever T moves the comparison prism across one half of the slit. The cylinder Q above the eye-piece contains the Amici prism. At the point N of the horizontal tube RN is the micrometer scale, illuminated by the mirror O. After raising the spring- catch L the upper part of the spectroscope may be turned round the pivot K, thus allowing of the adjustment of the eye-piece =66.--= (A full description accompanies each instrument.) 76. =Hand-Spectroscope=, Browning's, for spectroscopic examination of the blood =12.--= 76a. =Hand-Spectroscope= with comparison prism, mirror, and holder for vials =16.--= [Illustration: Thoma's Haemacytometer.] 77. =Thoma's Haemacytometer= consists of an object glass with carefully constructed cell, a ground absolutely plane coverglass and two pipettes for mixing the blood and saline solution used in the examinations. One of these pipettes, for estimating the number of red corpuscles is so graduated as to permit dilution of the blood 100 or 200 times as required; the other, for counting the white corpuscles (leucocytes), is graduated for dilution of the blood 10 or 20 times. The volume contents of the pipettes are most carefully determined and the depth of the cell is established by accurate micrometric measurement, thus permitting very exact observations by means of this instrument. (A full description with each instrument) =14.50= 78. =Mixing-Pipette for white corpuscles= =3.60= 79. =Mixing-Pipette for red corpuscles= =3.60= 80. =Thoma counting chamber, with coverglass= =5.75= 81. =Türck counting chamber with coverglass= =7.25= [Illustration: Counting chamber after Thoma after Türck.] [Illustration: Ehrlich's Eye-piece.] 82. =Ehrlich's Eye-piece= is provided with a diaphragm having a square opening, the size of which is regulated by a small lever. This eye-piece is designed to facilitate the estimation of the relative numbers of red and white blood corpuscles in dry preparations. Full directions accompany each instrument =12.--=