276 TECHNICAL MICROSCOPY. 



If cellular or granular elements in a preparation are imbedded 

 between fibrous ones, which latter are to be examined, the former 



may sometimes be removed by 

 the brush a method which is 

 frequently employed in animal 

 preparations. The specimen is 

 placed in a suitable medium on a 

 glass slide, and is lightly teased 

 with a brush, held vertically 

 (Fig. 155), until the liquid be- 

 comes disturbed and the tissue 

 FIG. 155. 



clears. This process is repeated 



several times if necessary, and the preparation is washed and 

 turned about, fresh liquid being added until at length no further 

 turbidity is seen. 



For the preparation of sections razors are generally employed ; all 

 other cutting instruments, such as double-edged knives, scalpels, &c., 

 are superfluous for botanical purposes, and in our experience their 

 value, even for animal substances, is very secondary. Those who 

 can use the razor skilfully will find it sufficient at any rate in the 

 majority of cases. The blade should be ground flat or hollow, 

 according to circumstances. For rather large sections through 

 woody formations, a flat knife, which does not bend when pressed 

 upon the nail, should be used, but for soft vegetable tissues hollow 

 razors with pliable edges. 



Before the actual cutting, the blade and the object should be 

 moistened, because dry-cut sections are usually less satisfactory. 

 Dry gelatinous substances, such as the thallus of many of the 

 lichens, should be treated as exceptions, as they do not offer the 

 necessary resistance when moist or distended ; in this case a mere 

 touch with the moist lip will suffice. In cutting, the knife must 

 not be pressed through like a wedge at right angles to the longi- 

 tudinal axis, but must rather be drawn through diagonally, in 

 order that the sectional surface may be as smooth and clean as 

 possible. 



If the preparations are so thin or so small that their manipula- 

 tion and the proper application of the knife are rendered difficult, 

 they must be supported whilst sections are being made. With 

 thin thread-shaped or lamella-like substances (leaves, &c.), several 

 may be placed one upon the other and then pressed between the 



