684 SUMMAKY OP OTJRBENT EESEARCHES RELATING TO 



in its downward excursion. An adjustable sector by the side of the toothed 

 wheel throws the pawl out of gear after a given radius of the wheel has been 

 turned through an arc embracing the desired number of teeth. This adjust- 

 ment is also effected before the block, containing the object to be cut, 

 reaches the edge of the knife. The adjustment for the next section is there- 

 fore effected while the surface of the block is not in contact with the under 

 side of the knife, so that no flattening or scraping effect is produced on the 

 surface of the block in its upward passage past the knife. 



The movement of the vibrating lever being arrested at each down 

 stroke at one point and the pawl which catches into the notches in the 

 toothed wheel being released at any desired point by the action of the 

 adjustable sector, it is possible to adjust the apparatus with great accuracy 

 for cutting sections of any desired thickness. If a given radius of the 

 wheel is moved through the arc embraced by a single tooth, sections are 

 cut, having a thickness of only 1/10000 of an inch, or • 0025 mm. — a 

 thickness which is only practically possible with paraffin imbedding and a 

 very keen razor. If more teeth are taken by the pawl, any thickness of 

 section is possible up to about 1/400 of an inch, or 0'0625 mm. (The 

 screw which adjiists the block for cutting has exactly fifty threads to the 

 inch, and there are two hundred teeth on the periphery of the toothed wheel* 

 The value of a single tooth is, therefore, 1/50 X 1/200 = 1/10000 in.). 



A freezing attachment, which has lately been appended to the appara- 

 tus, shows that frozen sections can be made with as great rapidity and 

 success as those cut from objects imbedded in the paraffin block, and very 

 nearly, if not quite, as thin. Other auxiliary apparatus makes it possible 

 to cut celloidin sections. This is effected by means of alcohol conducted 

 by a tube from a reservoir to the knife, over which the fluid will run and 

 drain into a tray below in such a way as not to come in contact with any 

 other parts of the machine. This tray fits into a recess in the side of the 

 bed-plate of the instrument just below the knife, and into this tray the 

 celloidin sections may be allowed to drop as fast as cut. 



The paraffin-holders are square and 7/8 in. in diameter, so that a 

 block of that size may very readily be sectioned. For the botanist, one of 

 these holders is provided with a movable side and screw for clamping 

 objects, so that rather tough stems may be firmly held between blocks of 

 cork, while the more delicate vegetable tissues, or such as must be im- 

 bedded in fresh carrot, soaked in gum and hardened in alcohol, may also 

 be firmly held for sectioning by the same device, provided the pieces of 

 carrot are first trimmed into the right shape. The same style of holder is 

 equally applicable for holding the corks — if properly trimmed — upon 

 which tissues are imbedded in celloidin or in gum. This style of holder 

 also enables one to imbed very long objects entire in paraffin — such as 

 earthworms — and to cut them as a single piece, provided the surrounding 

 paraffin is carefully trimmed so as to have two opposite sides parallel. 

 An object 6 in. long and 3/4 in. in diameter, imbedded in this way, may be 

 cut into an absolutely continuous series of sections without losing any 

 essential portions. This is accomplished by slipping the block through 

 the quadrangular clamp for the distance of 1/2 in. every time 1/2 in. of the 

 object has been cut off in the form of sections. 1/2 in. is the length of 

 block which can be cut at one time without readjusting the feed-screw 

 which moves the block and vibrating lever over towards the knife, the 

 whole being kept firmly in place against the face of the hollow screw by 

 a strong spring which presses against the end of the trunnion on the out- 

 side of the iron pillar on that side of the instrument where the knife is 

 fastened, so that all the sections are of exactly the same thickness, from 



