Production of Sections 265 



must be cut to allow immediate access of the fixative to the 

 ovules and nuclei. If you gather your specimen and do not 

 act at once, all the fixatives known to science applied with 

 the utmost cunning will not preserve for you mitotic figures 

 — will not preserve for you life-like stages in the histology 

 of your subject, but will merely give you representations of 

 post-mortem or pathological conditions. Eemember, then, 

 that for the representation of life-like histological struc- 

 tures, the utmost attention must be given to the very first 

 process of work — viz., fixation. 



Fixation. — Do not overfix, especially with the osmic and 

 chromic salts. The length of time and the best different 

 reagents required for fixing the various subjects can be 

 learned by experience and from the works of reference 

 already named. We will, however, say that, for general 

 work on nuclei and protoplasm, the beginner will find 

 Carnoy's acetic alcohol very useful for his first attempts. 

 It is made as follows, and keeps indefinitely : 



Absolute alcohol ... ... 350 c.e. 



Glacial acetic acid ... ... 150 ,, 



Use large quantities of fixative — say, 50 c.c. to object of 

 1 c.c. bulk. After fixing — say, for nuclei, two hours in 

 this mixture — it is important to wash out the acetic acid. 

 It may be well here to state that by fixing we mean the 

 instantaneous killing and coagulation of the albuminoids 

 and other histological elements, so that, having no time to 

 undergo a post-mortem or pathological change, the elements 

 may be preserved in life-like form. The subsequent harden- 

 ing enables the tissues to pass through the staining and 

 other processes without metamorphosis. 



The washing out of the acetic must not be done in 

 water, but in methylated spirit. A word on this spirit : 

 the ordinary methylated of the shops must not be used, 

 for this contains mineral naphtha and other substances. 

 Spirit methylated with wood-naphtha will have to be 

 purchased from a distillery under a permit from the 

 Custom authorities. 



