264 Modern Microscopy 



purchased with the sledge microtome, or added subse- 

 quently. 



Celloidin Embedding. — Another process, less used now 

 than in the past days of microtomy, is the celloidin em- 

 bedding process. This is a true microtome method, and 

 possesses some advantage for certain objects over the paraffin 

 method. Its great disadvantages are the slowness of the 

 process, and the skill necessary to cut sections of such tenuity 

 as can be accomplished with ease by the paraffin process. 

 The sections cut are isolated — i.e., you cannot cut a con- 

 tinuous ribbon of sections as by the paraffin method. True, 

 the isolated sections may be mounted upon the slide con- 

 tinuously by a complicated process, but the majority of us 

 live but threescore years and ten. 



The paraffin method, then, is the method par excellence 

 for most work. We will therefore confine ourselves to 

 a description of this process, confident that by its means 

 the student will be enabled to carry out the greater part, if 

 not all, of his researches into the minute. 



Collecting and Preserving. — The first attention must 

 be given to the collection and preservation of the objects to 

 be microtomed. These processes vary so considerably with 

 each department and subject that it is not possible here to 

 enter into the matter in detail. Animal histologists will find 

 much information in BoUes Lee's ' Microtomist's Vade- 

 Mecum '; botanists may advantageously refer to the useful 

 pages of ' Botanical Microtechnique,' by Dr. A. Zimmer- 

 mann. For instance, living organisms or portions of them 

 must be taken at the time of robust health, and killed and 

 fixed instantaneously by means of the substances best suited 

 for obtaining the results desired. If you wish to make a 

 preparation of mitosis from the embryo sac of some plant, 

 your specimen must be thoroughly healthy and vigorous. 

 The ovary must be cut and instantaneously placed in the 

 fixing fluid. It is important to see that the fixative can at 

 once reach the ovules ; consequently, it is not sufficient to 

 throw the whole ovary into the solution — the ovarian wall 



