51 



suitable size for the well of the microtome, removing, at the same time, all 

 extraneous matter, and all parts of which it is not desired to make sections. 



Stems, petioles, and peduncles should be cut into pieces about an inch 

 long. 



Leaves of Dicotyledons should include the mid-rib if possible. 



Boots and tubers should be first cut with a cork-borer into cylinders of 

 about | to f inch in diameter, taking care that the axis of the cylinder is at 

 right angles to the direction in which the sections are to be cut. 



2nd, Hard objects, such as woody stems, are placed in distilled water 

 for two or three days, changing the water every day, to dissolve out gummy 

 matters. 



3rd, They are placed in pure methylated spirit for three or four days, 

 changing the spirit every day, to dissolve out resinous substances. They 

 may then be placed in a mixture of equal parts methylated spirit and dis- 

 tilled water, until it is desired to cut them up. 



If any of the objects are still too hard, they must be soaked in distilled 

 water for a day or two, immediately before cutting. If this does not suffice, 

 they must be placed in hot, or even boiling, water, for as long as may be 

 necessary, the vessel containing them being kept in a warm place. 



4th. Soft tissues must be hardened in alcohol — dilute, strong, or even 

 absolute, as may be required. 



It must be remembered that these are only general rules. The experi- 

 ence gained by practice will enable special cases to be treated in an appro- 

 priate manner. 



By far the best substance in which to embed the object is carrot. It is 

 important that this should be quite fresh and crisp, so as to break short off, 

 without bending. If it is flabby it will not hold the object sufficiently firm ; 

 it may be preserved in good condition for a few day3 by being placed in 

 cold water, and kept in a cool place. 



A piece should be cut with a suitable punch to accurately fit the well of 

 the microtome, and the ends cut off square. It is then to be divided longi- 

 tudinally down the centre, and the object imbedded in it, so that, when the 

 two halves are placed together, the object may be rigidly supported on all 

 sides, without being unduly squeezed. The whole secret of successful im- 

 bedding lies in this. If the object be not sufficiently firmly held, or if it be 

 pressed too hard, in either case good sections cannot be cut. They will 

 either be of unequal thickness, owing to the material giving under the pres- 

 sure of the knife, or will be broken by the squeezing it has received. 



The plug of carrot containing the object is placed in the well of the micro- 

 tome, when it will be ready for cutting ; the microtome should be clamped 

 to the table, so that both hands are at liberty, and the object should be kept 

 flooded with a mixture of spirit and water. 



The stroke should be made from, never towards, the operator ; the razor 

 should be hollow ground, and must have been rubbed down on a hone until, 

 when placed on a level surface, every point of both back and edge touch at 

 the same time ; this is absolutely essential if we wish to cut good sections. 



As regards the thickness of the sections, they should generallv be of about 



