62 CYTOLOGICAL TECHNIQUE 



distorted mechanically or even destroyed. The coagulants and 

 non-coagulants thus compensate for one another's defects. 



The chief effect of acetic acid in these mixtures is the prevention 

 of excessive shrinkage. Tissues fixed in acetic acid alone swell, but 

 are greatly shrunken on subsequent dehydration. If, however, 

 they are stabilized in the swollen condition by the simultaneous 

 action of a fixative for proteins, the shrinkage seen in the final 

 preparation is far less. When acetic acid is used in mixtures at 5 % 

 or thereabouts, there is no necessity to add an indiff"erent salt. 

 Acetic acid also plays a part in the fixation of nucleoprotein, but 

 this is not important when the coagulant is chromium trioxide. 



A defect of Flemming is that the constituents penetrate at 

 different speeds. The most external part of the piece of tissue is 

 not capable of being dyed successfully, because osmium tetroxide 

 has exerted too powerful an eff'ect upon it (p. 49) ; the most in- 

 ternal part shows the effects of fixation by chromium trioxide and 

 acetic acid alone (apart from the blackening of lipid globules). In 

 the intermediate region, however, fixation is usually excellent. 

 Chromosomes are well fixed, as indeed one would expect; for the 

 famous German cytologist who designed the mixture did more 

 than anyone else to clarify the process of mitosis. The ground 

 cytoplasm preserves much of its homogeneity; various cyto- 

 plasmic inclusions, especially the idiozome, are very well shown. 

 Mitochondria are not necessarily destroyed, but as a rule they are 

 not easily shown after fixation by Flemming with full acetic. In 

 the study of these particular cytoplasmic inclusions the acetic acid 

 is commonly much reduced in amount^- or omitted.^"^- " 



HELLY (1903)9 7 



Distilled water 100 ml 



Mercuric chloride . . . . 5 g 



Potassium dichromate . . . . 2-5 g 

 Sodium sulphate . . . . . 1 g 



To 10 ml add 0-5 ml of formalin (neutralized by marble) immediately 



before use. 

 pH 3-7.^2 



The fixative may be washed out in acidified 50° o ethanol and iodized 



