FORAMINIFERA 



130 



FORMALIN 



ling and decanting. Dissolve ppt. in 

 just sufficient NH4OH, added drop by 

 drop, to almost completely dissolve it 

 leaving a few gray granules. Heat to 

 steaming to drive off excess NH3 and 

 cool to 50 °C. Reduce in 1% formalin 

 2 min. Wash in tap water. Tone2min. 

 in 0.2% aq. gold chloride. Wash. Tone 

 in 5% aq. sodium thiosulphate. Coun- 

 terstain with hematoxylin-Van Gieson. 

 Reticulum, black; collagenic fibers, 

 Vermillion; cytoplasm, yellow; and 

 nuclei, brown. 



(2). Silver method for nerve fibers in 

 paraffin sections (Foot, N. C, Am. J. 

 Path., 1932, 8, 769-775). This is a 

 modification of Cajal's technique. Fix 

 in fresh Carney's Fluid for 24 hrs. 

 Transfer to absolute alcohol for 1-2 hrs., 

 clear in chloroform and imbed in par- 

 affin. Remove paraffin from sections in 

 usual way. Treat with 2 parts pyridine 

 and 1 part glycerol for 1-12 hrs. Wash 

 in 95% alcohol and then in aq. dest. to 

 remove most of pyridine. A trace re- 

 maining does no harm. Immerse in 

 10% aq. silver nitrate at 37 °C. for 12 hrs. 

 or so covering container to avoid evapo- 

 ration. Wash in 2 changes aq. dest. 

 Place in 5% aq. neutral formalin con- 

 taining 0.5% pyrogallol in which sections 

 become yellow-brown, 20 min. Wash 

 under tap. Tone in 1:500 aq. gold 

 chloride, 5 min. (Nuclear precision is 

 improved and glacial impregnation is 

 made less intense if 2% glacial acetic is 

 added to gold solution). Then place in 

 2% oxalic acid containing 1% neutral 

 formalin for 5 min. Wash at the tap and 

 transfer to 5% aq. sodium thiosulphate 

 for 5 min. Finally washagain in running 

 water, dehydrate, clear and mount. 

 Foot also recommends Rogers' technique 

 practically as given by him (Rogers, 

 W. M., Anat. Rec, 1931, 49, 81-85) 

 The idea of intensifying the gold toning 

 with oxalic acid he credits toLaidlaw, 

 G. F., Am. J. Path., 1929, 5, 239-247. 

 See general remarks on Silver Methods. 



Foraminifera, see Carpenter, W. B. The 

 Microscope and its Revelations, Lon- 

 don, 1901. 



Formaldehyde is a gas (HCOH) soluble to 

 40% in water producing a solution which 

 is termed commercial formalin or for- 

 mol. See Formalin. 



Formalin (Formol) is a 37% aq. solution of 

 the gas, formaldehyde. Solutions em- 

 ployed as fixatives and preservatives 

 are made in terms of the percentage of 

 formalin, not of formaldehyde. Thus, 

 a 10% solution of formalin (formol) is by 

 convention 10 cc. of formalin plus 90 cc. 

 of water. It is not however 10% for- 

 maldehyde. (Obviously to dilute 10 cc. 

 cone, hydrochloric acid with 90 cc. of 



water would not give 10% hydrochloric 

 acid because cone, hydrochloric acid is 

 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. Lillie (p. 28) specifies a neutral 

 buffered formaldehyde solution (pH 

 70) as follows: 37-40% formaldehyde 

 solution, 100 cc; water, 900 cc; acid 

 sodium phosphate, monohydrate, 4 gm. ; 

 anhydrous disodium phosphate, 6.5 

 gm. Constant pH is desired. Unless 

 neutral formalin is specified and the 

 manner of neutralization, it is best 

 simply to use the fairly pure product 

 which now can readily be obtained. 

 Experiments by Davenport, H. A., 

 Stain Techn., 1934, 9, 49-52 show that 

 as a neurological fixative slightly acid 

 formalin is somewhat better than neu- 

 tral formalin. A few of the manj^ de- 

 mands for formalin as a fixative will 

 be found under: 



Alizarin red S 



Alveolar pores 



Amyloid 



Argentaffine cells 



Arsenic 



Articular nerve ter- 

 minals 



Bile pigments 



Bismuth 



Bodian 



Bone 



Buzaglo 



Cajal's brom-formol 



Cartilage 



Chitin 



Chloride 



Chorioallantoic mem- 

 brane 



Christeller-Koyama 



Chromaffin reaction 



Color preservation 



Connective tissue cells 



Dopa oxidase 



Fatty acids 



Fluorescence micros- 

 copy 



Foot 



Frozen sections 



Giemsa staining 



GUa staining 



Gomori 



Gordon 



Grieves 



Johnson's neutral red 



Kinney 



Krajian 



Liebermann - Burch- 



ardt 

 Madder staining 

 Mallory's connective 



tissue stain 

 Microglia 

 Mucus 



Nile blue sulphate 

 Perdrau 

 Pia mater 

 Romieu 



Schultz cholesterol 

 Sebaceous glands 

 Silver citrate 

 Smith- Dietrich 

 Spirochetes 

 Vorhoeff 

 Weigert-Pal 

 Weil 

 Wilder 



