[Illustration: FIG. 37.--Minot Rotary Microtome] The =Minot rotary microtome= (Fig. 37) has a fixed knife, held in position by two pillars, and a movable object-carrier. The object is firmly secured by a clamp, and it is raised by a micrometer screw. The screw is attached to a wheel having five hundred teeth on its periphery. A pawl is adjusted to the teeth in such a way that, when moved by turning a wheel to which it is attached, specimens varying from one to twenty-five microns in thickness may be cut, according to the way the adjusting disk is set. When the mechanism has been regulated and the object adjusted for cutting, it is only necessary to turn a crank in cutting sections. CARE OF MICROTOMES When not in use, microtomes should be protected from dust, and all parts liable to friction should be oiled. Microtome knives should be honed as often as is necessary to insure a proper cutting edge. After cutting objects, the knives should be removed, cleaned, and oiled. It should be kept clearly in mind that special knives are required for cutting collodion, paraffin, and frozen and woody sections. The cutting edges of the different knives vary considerably, as is shown in the preceding cuts. CHAPTER V REAGENTS Little attention is given in the present work to micro-chemical reactions for the reason that their value has been much overrated in the past. A few reagents will be found useful, however, and these few are given, as well as their special use. They are as follows: LIST OF REAGENTS =Distilled Water= is used in the alcohol, glycerine, and water mixture as a general mounting medium. It is used when warm as a test for inulin and it is used in preparing various reagents. =Glycerine= is used in preparing the alcohol, glycerine, and water mixture, in testing for aleurone grains, and as a temporary mounting medium. =Alcohol= is used in preparing the alcohol, glycerine, and water mixture, in testing for volatile oils. =Acetic Acid=. Both dilute and strong solutions are used in testing for aleurone grains, cystoliths, and crystals of calcium oxalate. =Hydrochloric Acid= is used in connection with phloroglucin as a test for lignin and as a test for calcium oxalate. =Ferric Chloride Solution= is used as a test for tannin. =Sulphuric Acid= is used as a test for calcium oxalate. =Tincture Alkana= is used when freshly prepared by macerating the granulated root with alcohol and filtering, as a test for resin. =Sodium Hydroxide=. A five per cent solution is used as a test for suberin and as a clearing agent. =Copper Ammonia= is used as a test for cellulose. =Ammonical Solution of Potash= is used as a test for fixed oils. The solution is a mixture of equal parts of a saturated solution of potassium hydroxide and stronger ammonia.