A METHOD OF CONTROLLING THE TEMPERATURE OF 
THE PARAFFIN BLOCK AND MICROTOME KNIFE 
CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 188 
W. J. G. Lanp 
(WITH TWO FIGURES) 
The successful production of a continuous ribbon of paraffin 
depends chiefly on the temperature of the block in which the object 
is imbedded, and of the microtome knife. The hardness and size 
of the object may of course affect the ribbon, but if the object 
is small, not refractory, and completely infiltrated, the effect is 
practically negligible. If the temperature of the knife and block 
is made sufficiently low, very thin sections can be cut without 
unduly compressing the object, regardless of the melting point 
of the paraffin. 3 : 
With paraffin of a given melting point there is a definite tempera- 
ture at which the block and knife must be kept in order to produce 
a continuous ribbon of definite thickness without injurious com- 
pression of the sections. If the microtome is set for thinner sections 
without lowering the temperature of the knife and block, the sec- 
tions are compressed more and more as they are made thinner, 
until a point is reached where the tissues are crushed out of all 
resemblance to their original condition. This crushing of. the 
sections has in some instances resulted in erroneous interpretation 
of structures even by otherwise competent investigators. Again, 
if the microtome is set for thicker sections and the temperature of 
the knife and block is not correspondingly raised, excellent sections 
result, but their edges refuse to weld and they come away singly, a 
source of much trouble when an absolutely unbroken series is 
required. If the thickness is further increased, the sections come 
away rolled so tightly that in some instances they cannot be 
unrolled even by floating on warm water. 
In practice, when thick sections (to-20 u) are wanted, the 
object is imbedded in paraffin bee at 45-52°C. If thinner 
Botanical Gazette, vol. 57] ~ [520 
