MICROTOMES. 



389 



the 



The head of the embryo is to be toward the lower edge of the ribbon. 



The series is to begin with the ventral side. 



In cutting, the left side of the embryo must strike the knife first. 



In mounting leave space for the label at the left-hand end of the slide. Keep 



sections in the order cut. Arrange them on the slides in the sequence of 



ordinary written lines. 



Microtomes. 



There are many forms of microtome which may be used with good results 

 and which will work very satisfactorily for making sections of small objects. The 

 cutting of larger objects, such as pig embryos of from 15 to 20 mm., and of pieces 



FIG. 261. THE PRECISION MICROTOME. 



of the uterus or other organs, is more difficult, and microtomes which work satis- 

 factorily with small objects often fail to give good even sections of more difficult 

 objects. For embryological work a microtome ought, therefore, to be selected 

 which will give perfectly regular sections in long series of any desired thickness 

 from i/* up to 25/4. It is also desirable for economy of time to have a micro- 

 tome which works automatically. These considerations lead the author to recom- 



