124 Animal Microlooy 



and left sides and dorsal and ventral surfaces in proper relation to the 

 observer, mount the object in such a way that in cutting the knife will 

 enter it on the right side and at the anterior end. In mounting, each 

 section (or strip of ribbon) is turned over and mounted with its posterior 

 face toward the observer and its ventral edge toward the upper edge of 

 the slide. Leave room at one end of the slide (see chap, vi, I, 10) for a 

 label and also a small margin at the opposite side. 



6) To get proper orientation of frontal sections (sections lengthwise 

 of the object in a plane including right and left sides) arrange the object 

 so that the knife will enter it on the right side and slice off the dorsal 

 surface first. Mount sections, with their posterior ends toward the 

 upper edge of the slide placing the first section of the series to the left 

 end of the upper row. This throws left and right, dorsal and ventral 

 into their proper position as viewed through the compound microscope 

 and the observer looks from the dorsal toward the ventral aspect of 

 the object. 



c) To mount sagittal sections (sections lengthwise of the object in a 

 plane including ventral and dorsal sides) arrange the object in such a 

 position that the knife enters the ventral surface and slices off the left 

 side first. Turn the section (or ribbon) over and mount with the pos- 

 terior end toward the upper edge of the slide, placing the first section 

 of the series at the left end of the upper row. Through the compound 

 microscope, the observer views the object from the right toward the left. 

 The head will appear to be toward the upper end of the slide, the dorsal 

 surface toward the left. 



It is frequently advantageous to have the imbedding mass trimmed 

 unsymmetrically by leaving the edge which first comes in contact with 

 the knife longer than the opposite edge. One may thus readily discover 

 if a section or part of a series has been accidentally turned over. 



13. Orientation of Objects in the Imbedding Mass so that sections can 

 be cut accurately in definite planes is frequently difficult to accomplish. 

 The following methods are useful in many instances: 



I. For paraffin sections. With a soft pencil rule the strip of 

 paper which is to be used for making the imbedding-box into small 

 squares or rectangles. After imbedding, upon removal of the paper a 

 copy of the pencil marks will be found upon the block of paraffin. If 

 the object has been arranged in the melted paraffin with reference to 

 these lines, it is easy so to arrange the block in the microtome as to cut 

 the object along any desired plane. It is frequently an aid to orientation 

 by this method to have one of the central ruled lines broader than the 

 others, or double. 



Small objects which cannot conveniently be oriented in melted par- 

 affin may be properly oriented and fixed to a small strip of paper ruled 



