PRIMARY fixatives: COAGULANTS 95 



Canada balsam. No other fixative studied by Ross ^^^ gave so 

 much shrinkage of cells in final preparations. There is evidence 

 that nuclei are not so badly shrunk as whole cells. ^^^ 



Hardening. Ethanol hardens tissues extremely, more so than any 

 other fixative except acetone. Wetzel's ^^^ figure representing 

 rigidity (elasticity) is about 4600 (about 20 times as great as the 

 figure for chromium trioxide). 



Immediate effects on particular constituents of the cell, A coarse 

 coagulum is produced throughout the cytoplasm; mitochondria 

 are destroyed; lipid globules tend to fuse and may dissolve. A 

 coarse coagulum appears also in the nucleus; the nucleolus is 

 shrunken. 



Methods of washing out. Ethanol is miscible in all proportions 

 with toluene and similar antemedia for paraffin embedding, and 

 also with ether (and with water). It follows that no special washing 

 out is necessary. 



Effect on dyeing. Ethanol has less eflPect on the dyeing of proteins 

 than most fixatives have. Albumin remains readily colourable by 

 both basic and acid dyes: protamine, strongly basic before fixation, 

 remains acidophil afterwards. ^^^ Fixed cytoplasm reacts to dyes 

 like fixed albumin; chromatin is rendered strongly colourable by 

 basic dyes, but its distribution in the cell is not stabilized, and 

 ethanol is therefore a very poor fixative for chromosomes at all 

 stages. 



Effects on the histological picture seen in paraffin sections. By 

 itself, ethanol is a poor fixative (grade IV). Cellular aggregates tend 

 to shrink apart from one another, leaving rather large spaces in 

 between; cells also tend to separate from one another; cytoplasm 

 contracts strongly. Red blood-corpuscles are not badly fixed, 

 partly because haemoglobin is preserved (as kathaemoglobin ^^^), 

 partly because the chief distortion to w^hich they are subject is 

 swelling, and ethanol prevents this. Nuclei are fixed without much 

 distortion of shape; a nuclear network is not produced. Chromo- 

 somes are not distinctly seen. 



The cytoplasm often contracts in such a way that it is piled up 

 against the cell-membrane on the side opposite to that from 

 which the fixative penetrated. Any glycogen present in the cell 

 will be found in the displaced mass of cytoplasm. The contents 

 of the nucleus are often piled up against the nuclear membrane 

 in the same way. This curious orientation of the protoplasm has 

 not been satisfactorily explained. It is presumably connected with 



