FLUORESCENCE MICROSCOPY 



100 



FORMALIN 



in ultraviolet light. Such substances 

 are called fluorochromes. Sections of 

 tissue are immersed in such substances 

 for a short period of time before being 

 examined. Examples of the use of these 

 fluorochromes are found in papers by 

 Haitlinger (loc. cit.), Jenkins (loc. cit.), 

 Clark and Perkins (W. M. and M.E., J. 

 Am. Chem. Soc, 1932, 54, 1228-1248), 

 Lewis (M. R., Arch. f. exp. Zellf., 1935, 

 17, 96-105) and Popper (H., J. Mt. 

 Sinai Hosp., 1940, 7, 119-132). A good 

 account of fluorescence microscopy of 

 insects is given by Metcalf, R. L.. and 

 Patton, R. L., Stain Techn., 1944, 19, 

 11-27. See Vitamin A, Tubercle Bacil- 

 lus, Cell Injury, Uranium, Porphyrins, 

 etc. 



Fluorescence Spectra. The technique in 

 some detail is described for 3:4-Benz- 

 pyrene by Hieger, I., Am. J. Cancer, 

 1937, 29, 705-714 who thinks that the 

 photographs of the spectra can well be 

 studied by simple visual examination. 



Fluorescent Blue, see Resorcin Blue. 



Fluorescent X. A special type of reduced 

 neutral red (Clark, W. M. and Perkins, 

 M. E., J. Am. Chem. Soc, 1932, 54, 

 1228-1248) employed for tissue cultures 

 (Lewis, M. R., Arch. f. exp. Zelf., 

 1935,17,96-105). 



Fluorine, see Atomic Weights. 



Fluorochromes. See Fluorescence micros- 

 copy. 



Foods. The examination of foods to ascer- 

 tain their suitability for human con- 

 sumption involves not only organolep- 

 tic tests (use of unaided senses, sight, 

 smell, taste, etc.), but direct micro- 

 scopic examination and certain cul- 

 tural, experimental feeding, and other 

 tests. The techniques for adultera- 

 tions, bacteria, fungi, crystals, spores, 

 parasites and so on are usually the 

 routine ones. However, much time 

 will be saved by knowledge as to what 

 to look for in each case, how to look and 

 the best means of making the observa- 

 tions accurately quantitative (Schnei- 

 der, A., The Microbiology and Micro- 

 analysis of Foods. Philadelphia: P. 

 Blakiston's Son & Co., 1920, 262 pp.). 



Foot's Methods. 1. Rapid silver impreg- 

 nation of reticular fibers (Foot, W. C, 

 J. Tech. Meth., 1929, 12, 117-119). 

 Fix in 10% formalin (not necessarily 

 neutral), Zenker's, Bouin's or Helly's 

 fluids, 24 hrs. Make paraffin sections. 

 Remove mercury, if present, with iodine. 

 Treat with 0.25% potassium permanga- 

 nate, 5 min. and 5% oxalic acid, 10 min. 

 Wash in aq. dest. Impregnate 15 min. 

 in following silver solution at 50 °C. : Add 

 40 cc. 5% aq. NajCOs to 10 cc. 10% aq. 

 AgNOs. Let precipitate settle. De- 

 cant supernatant fluid. Make up to 



50 cc. with aq. dest. Shake, repeat sett- 

 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. Tone 2 min. 

 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 Carnoy'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 wash again 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 to Laidlaw, 

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

 See general remarks on Silver Methods. 



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 



