FORMALIN 



101 



FROZEN SECTIONS 



not 100% so that this practice cannot be 

 extended.) Formerly it was necessary 

 to neutralize commercial formalin in 

 various ways, and it still is for special 

 purposes. The best way to obtain 

 neutral formalin is to distil. Atkins 

 (Lee, p. 61) advises addition of borax 

 to the diluted formalin until it shows a 

 good red color with phenolphthalein or 

 slaty blue with thymol blue. Others 

 simply add a little calcium, sodium, 

 magnesium or even lithium carbonate. 

 Obviously the addition of such minerals 

 greatly complicates the problem when 

 formalin is employed with alcohol as a 

 fixative preliminary to microincinera- 

 tion. Unless neutral formalin is speci- 

 fied and the manner of neutralization, 

 it is best simply to use the fairly pure 

 product which now can readily be ob- 

 tained. Experiments by Davenport, 

 H. A., Stain Techn., 1934, 9, 49-52 show 

 that as a neurological fixative slightly 

 acid formalin is somewhat better than 

 neutral formalin. A few of the many 

 demands for formalin as a fixative will 

 be found under : 



In combination with other reagents 

 formalin is also a good fi.xative cf. For- 

 malin-Zenker in which formalin is sub- 

 stituted for acetic acid, Bouin, Regaud's 

 Fluid and many others. Since, how- 

 ever, formalin is a strong reducing agent 

 mixtures of which it is a part are un- 

 stable so that it must be added immedi- 

 ately before use. As ^lallory (p. 40) 



points out, formalin also has certain 

 disadvantages. It is inferior to alcohol 

 as a preservative for iron and other 

 pigments. It often changes the color of 

 bile concretions from yellow to green and 

 it may produce in the tissues a trouble- 

 some brown-black finely divided crystal- 

 line precipitate from laked hemoglobin. 

 He advises removal of this precipitate 

 by treating sections for 30 min. in 75% 

 alcohol, 200 cc; plus 25^28% ammonia 

 water, 1 cc. (Schridde's method), or for 

 10 min. in 80% alcohol, 100 cc. plus 1% 

 aq. potassium hydroxide, 1 cc. (Vero- 

 cay 's method ) after either of which they 

 are washed thoroughly in water before 

 placing in 80% alcohol and staining. 

 When employed as a preservative con- 

 centration of formalin should be 4%. 



Formalin-Alcohol, see Alcohol-Formalin. 



Formalin-Zenker. Zenker's fluid modified 

 by substituting 5% formalin in place of 

 the 5% acetic acid. It is also known 

 as Helly's fluid and Zenker-formol. 

 This is one of the three major routine 

 fixatives the others being Zenker and 

 Bouin. See Acid Fast Bacilli, Alveolar 

 Pores, Arteries, Basal Bodies, Brazilin- 

 Wasserblau, Mucus, Goodpasture's 

 Method, Methyl-Green Pyronin. In 

 some cases 10% formalin is inserted 

 instead of 5%. 



Formalose see Formalin, 



Formamide of Eastman Kodak Co. is a sub- 

 stance, called a "modifier", which when 

 added in 10% to 50% alcohol improves 

 fixation and staining of peripheral nerve 

 (Bank, E. W. and Davenport, H. A., 

 Stain Tech., 1940, 15, 9-14). 



Formol is a synonym for formalin. 



Formol-Miiller. This is 1 part of formol to 

 10 parts Mailer's fluid. 



Formol-Nitric fixative. 3 parts 10% for- 

 malin and 1 part 10% nitric acid. This 

 has, according to McClung, proved very 

 valuable for chick embryos. 



Formol-saline is the fluid resulting when 

 formalin is diluted with isotonic salt 

 solution (presumably 0.85% aq. sodium 

 chloride) instead of with aq. dest. It is 

 not advised as a fixative. 



Fowl Pox, see Borrel Bodies. 



Fractures. Vital staining with Alizarin 

 Red S (Schour, et al., J. Dent. Res., 

 1941,20,411-418). 



Fragility Tests. Micro for erythrocytes 

 (Kato, K., J. Lab. & Clin. Med., 1940, 

 26, 703-713. See Capillary Fragility 

 Tests. 



Freezing, see Revival after. 



Freezing and Drying, see Altmann-Gersh. 



Frozen Sections. These are of great value 

 when preparations must quickly be 

 made and when methods of alcoholic 

 dehydration before sectioning are contra- 



