82a. =Apparatus= for the clinical determination of the alcalinity of the blood, after Prof. C. S. Engel. The following parts compose the apparatus: 1) a capillary pipette so graduated as to permit the dilution of 0,05 cc. blood from the finger, up to 5 cc. with distilled water. 2) a beaker, for the reception of the diluted blood. 3) a burette mounted on stand, capacity 10 cc. Full directions accompany each outfit. Price in box =8.--= =Micrometers.= [Illustration: Screw Micrometer Eye-piece.] 83. =Screw-micrometer eye-piece= for accurate measurement of large objects. Between the eye lens and the collecting lens of a Huyghenian ocular there is a millimeter scale etched on glass, above which is a moveable indicator whose position is controlled by a micrometer screw to which a graduated drum is attached. The value of each graduation on the drum (about 1/20 of the micrometer value of the objective) must be determined for each combination of ocular and objective by means of the stage micrometer. The eye lens of the ocular is moveable to permit accurate focus upon the scale. The apparatus slips into the tube of the microscope like any ordinary eye-piece and is fixed in position by a thumb-screw at the side =20.--= 84. =Micrometer eye-piece.= The mount unscrews in the centre to permit the introduction of the micrometer scale. The eye lens is moveable to permit of accurate focus on the scale =4.--= 85. =Glass-Micrometer for the eye-piece=, to drop on the diaphragm of the eye-piece. Scale of 5 mm divided into 100 parts =2.50= 86. =The same=, 10 mm divided into 100 parts =2.--= 87. =Stage-Micrometer=, 1 mm divided into 100 parts etched on glass =3.75= 88. =Stage-Micrometer=, photographed on glass, 2 mm divided into 200 parts =1.40= 89. =Eye-piece Micrometer=, divided into squares for counting scattered objects in the field. Mounted. Distance between the lines 0,5 mm =2.--= 90. =Glass slide with cell= 2/10 mm deep, with ocular micrometer No. 89, in box =3.25= 91. =Glass slide with cell= the floor of which is divided into squares, 1/400 square mm each, in box =4.--= =Drawing Apparatus.=