44 Botanical Microtechnique 



TEMPERATURE FACTORS 



Cutting is influenced 1)\ the temperature of the paraffin block, 

 of the knife, and of the room. If the temperature of one or more of 

 these factors is too high, compression of the sections occurs on impact 

 with the knife. If the temperature is too low, the sections may curl, 

 or successive sections may not adhere and thus fail to form a ribbon. 

 Thick sections are relatively more tolerant to higher working tem- 

 peratures than are very thin sections. A heavy microtome knife per- 

 mits a higher temperature than does a razor blade. If the temperature 

 is too high for the grade of paraffin being cut, cool the mounted 



Fig. 6.2— Methods of oricntiiio ol)jc(ts of various shapes: A, a leaf iiioimtcd for 



cross sections; B, a small stem or other cylindrical organ mounted for cross sections; 



C, for longitudinal sections; D and E, sectors mounted for cross sections; F, sector of 



large herbaceous stem mounted for radial sections. 



paraffin block and the knife or ra/or-blade holder in a jiaii ol ice 

 water. .Align the tissues and knife in the niicioiome cjuickh, and ciU 

 sections until the parallm becomes too soft, when the cooling should 

 be repeated. Knife cooling devices are described by johansen (I*) 10). 

 If a refrigeration loom is a\ailable. j)erfe(t control is possible by 

 setting lip the microtome in the (old looiii and warming a /one 

 around the knife with a desk laiii|). The author's department has 

 a cooled mic lotome loom with a floor space of 5 b\ 7 ieet antl a height 

 of <S Icct. A small compressor is mouiUed abo\e the loom on a hea\y 

 false ceiling. (Pooling coils are suspended on the (ciling. Ciravit) cool- 

 ing proxides a thei tnostatically contiolled constant temjH-rature of 

 ()()°F. Two mic lotonies and two sets ol accessories are pro\ided. and 

 two operatois have ample space. This room makes the research work- 



