8 Methods in Plant Histology 



knife next the object after every section. Unless this be wiped off, 

 the face of the block is dragged across it and the next section is 

 damaged even before it is cut. The side of the knife next the object 

 should be wiped with the finger, theoretically after every section. 

 It is very inconvenient to wipe the knife in a rotary microtome. 

 Another advantage of the sliding type is easy to feel but difficult to 

 describe: in the rotary microtome the stroke is so automatic that 

 there is little room for skill, but in the sliding microtome, with one's 

 hand on the sliding block, little variations in the stroke, variations 

 which become instinctive, give the expert a control not yet attained 

 in the rotary forms. 



Amateurs, and even professional botanists who have little 

 aptitude in the use of machines, had better rely upon the rotary 

 microtome. However, no better comment on the comparative merits 

 of the two forms could be given than the practice of an expert 

 technician in our own laboratory, who uses a rotary microtome when 

 making sections for ordinary class work, but who turns to a sliding 

 microtome of the Jung-Thoma pattern when cutting sections for 

 his own research. 



Attempts have been made to combine the advantages of the 

 sliding and rotary types. The " Precision Microtome," made by 

 Bausch & Lomb, has found favor in some circles. It has the sliding 

 movement, allows an oblique position of the knife, and is operated 

 like a rotary microtome. Recently, a much-improved microtome, 

 made by the Spencer Lens Co., has been winning favor. It is a 

 rotary, but even surpasses the sliding microtome in precision and 

 stability. Its effectiveness depends, in large measure, upon its 

 simple but rigid clamp for holding the object. This microtome, 

 fitted with Dr. Land's apparatus for cooling both the knife and the 

 paraffin block, is shown in Fig. 4. Streams of ice water flow under 

 the knife and through the hollow block to which the paraffin is 

 fastened. From paraffin with a melting-point of 52 C., or even 

 somewhat less, uniform ribbons 1 n in thickness can be secured. 

 If material has been imbedded in paraffin of 52 C. and it should 

 be desirable to cut sections at 15 /* to 20 /z, warm water can be 

 used. 



