94 FIXATION 



is no measurable denaturation below — 15° C. It slowly gelatinizes 

 histones.^^^ It does not denature zein or gliadin, nor does it stabil- 

 ize gelatine gel against solution by warm water. It converts 

 haemoglobin into kathaemoglobin ; ^^^ that is to say, it denatures 

 the globin without splitting off the haem. 



Ethanol is a non-coagulant of nucleoprotein. Nucleic acids are 

 precipitated from solution, ^^^'^^^ but not rendered insoluble in 

 water. 



Reactions with lipids. Ethanol does not fix lipids in the sense of 

 rendering them insoluble in lipid-solvents. 



Tripalmitin and tristearin are almost insoluble in cold ethanol, 

 triolein somewhat soluble; similarly palmitic and (especially) 

 stearic acid have only slight solubility in the cold fluid, while oleic 

 acid is readily soluble. Cholesterol is slightly soluble, the common 

 cholesteryl esters nearly insoluble. Lecithin is soluble ; the ethanol- 

 amine and serine esters of phosphatidic acid, together constituting 

 'cephalin', are insoluble, except in the presence of lecithin. 

 Sphingomyelin and the cerebrosides are insoluble. ^^^' ^^ Plasmalo- 

 gen is soluble in ethanol, but when associated with elastic fibres 

 it is not extracted by this solvent. ^^^ 



Thus among the common lipids, only triolein, oleic acid, 

 lecithin, and plasmalogen show more than slight solubility in cold 

 ethanol. Most lipids are soluble in hot ethanol, but this is not used 

 for fixation. 



Dilute ethanol is an 'unmasking' agent, capable of splitting lipids 

 off from certain lipoprotein complexes. ^^^ 



Reactions with carbohydrates. Ethanol does not fix carbo- 

 hydrates. Glycogen is insoluble in it and is therefore precipitated 

 unchanged. 



Rate of penetration. Ethanol penetrates slowly into clotted 

 blood-plasma,^^^ but it goes rather quickly into tissues. ^^^' ^^^' ^^^ 

 Tellyesniczky's ^^^ and Seki's ^^^ results with mammalian liver 

 agree closely. The K-value obtainable from their data is almost 

 exactly i-o. 



Shrinkage or swelling. Ethanol shrinks gelatine/albumin gel 

 more strongly than any other fixative except acetone. ^^ It also 

 shrinks whole livers strongly, though not so much as chromium 

 trioxide and picric acid do.^^ It shrinks Arbacia eggs to less than 

 half their original volume. The primary spermatocytes of Helix 

 aspersa are shrunk to 19% of their original volume when paraffin 

 sections of ovotestes fixed in ethanol have been mounted in 



