166 IMBEDDING METHODS. 



CHAPTER XIV. 



IMBEDDING METHODS INTRODUCTION. 



271. A Word on Microtomes. It is no part of the purpose of 

 this work to discuss instruments, yet a word on this subject 

 may be helpful to the student. The freezing microtome so 

 generally employed in England is less than any other form 

 adapted to the wants of the zoologist. Very thin sections can 

 be obtained by it more readily than with any other microtome, 

 but they are of little use when obtained. The relations of the. 

 parts of the organs are deranged by the freezing and by the 

 thawing, and the aqueous nature of the process prevents it 

 from being readily applicable to the mounting of series of sec- 

 tions. The microtome of the zoologist, therefore. (I am not 

 writing merely for pathologists or for dilettanti), must be an 

 imbedding microtome. The two most important points to be 

 attended to in the choice of such a microtome are the object- 

 holder and the knife motion. The object-holder should never, 

 as in some forms, be a well in which the imbedded object is 

 raised by a screw j the principle of construction should always 

 be that the object-holder be raised in its entirety by the screw, 

 not the object alone. The knife motion should always be 

 mechanical, the knife being guided by a mechanism giving 

 the required precision of stroke. And the object-holder should 

 be fitted with mechanical motions allowing of the orientation 

 of the object in all three directions of space. This is a most 

 important point ; such an object-holder is absolutely necessary 

 in many delicate morphological researches. 



Amongst microtomes fulfilling these conditions various 

 forms will be found almost equally convenient. Zeiss makes 

 a good one ; Schanze, of Leipzig, makes a good one ; Keichert, 

 of Vienna, makes a good one. All these are relatively cheap, 

 and, being at the same time perfectly efficient for easy work, 

 may be recommended. Amongst more precise instruments 



