RELIEF METHODS 



305 



RETICULAR FIBERS 



(Jordan, H., Am. J. Anat., 1925, 34, 

 427-443). 



Relief Methods, see Negative Stains. 



Replacement of Tissue to take the place of 

 that worn out or lost can now be 

 measured more accurately. Though 

 some signs of youth and age of cells 

 can be detected (Chapter 24 in Cowdry, 

 E. v., Problems of Ageing. Baltimore: 

 Williams & Wilkins, 1942, 936 pp.), 

 it is not so easy to determine the per- 

 centage actually dying as the per- 

 centage of new cells produced to replace 

 them by counting mitoses. Using whole 

 mounts of separated human Epidermis 

 from foreskins removed by circumcision 

 Cooper, Z. K., and Schiff, A., Proc. 

 Soc. E.xp. Biol. & Med., 1938, 39, 323- 

 324 have discovered that the produc- 

 tion of new cells is rhythmic being 

 greatest at night and least by day. To 

 obtain material, as they did every hour 

 of the day and night, of other human 

 tissues seems impossible. If one wishes 

 to investigate rate of cellular replace- 

 ment in internal less accessible tissues 

 that are replaceable, take advantage of 

 the fact that the drug, colchicine, per- 

 mits cells to enter mitosis but arrests 

 the process usually in themetaphase. 

 In consequence of this experimental 

 summation many more mitoses can be 

 counted in a given specimen than would 

 be found if cell division had been 

 completed as usual (See Mitosis for 

 the necessary controls). There are no 

 special means for the study of replace- 

 ment of Fibers but careful use of avail- 

 able techniques will probably yield 

 data as to whether the fibers are newly 

 formed or old and practically useless. 

 Phj'sico-chemical methods are how- 

 ever promising when backed by histo- 

 logical researches. Thus the new bone 

 formed, during the time that Madder, 

 or better Alizarin Red S, is made avail- 

 able in the circulation can be measured. 

 In adult animals, assuming that the 

 amount of bone remains approximately 

 constant, it can be concluded that the 

 breakdown is at the same rate and in 

 this round about way arrive at a figure 

 for replacement. 



Some fats can be conveniently colored 

 with fat soluble dyes which they retain 

 on ingestion and after incorporation in 

 the fatty depots of the body. It should, 

 therefore, be possible to keep animals at 

 a fairly constant weight on a diet con- 

 taining a certain amount of fat, to sub- 

 stitute for this fat stained fat of the 

 same sort without increasing their 

 weight and to estimate the ratio of stained 

 to unstained fat after a definite interval 

 of time — in other words the replace- 

 ment. Other possibilities are to employ 



for the test a fat of melting point quite 

 different from the native body fat of the 

 animals; and fatty acids tagged with 

 radioactive isotopes, see Fatty Acids. 

 The radioactive isotopes, particu- 

 larly those of Phosphorus and Iron give 

 somewhat similar clues. The amount of 

 radiophosphorus, for example, accumu- 

 lating in any particular tissue can be 

 accurately determined. If the supposi- 

 tion is justified that the total amount of 

 phosphorus (radioactive and non -radio- 

 active) remains about the same, then 

 non -radioactive phosphorus must be lost 

 at the rate that the radiophosphorus 

 enters. It is too soon however to pre- 

 dict what this possible line of investiga- 

 tion with the isotopes will show. See 

 Radiophosphorus. 



Resazurin, a compound used as an o.xida- 

 tion-reduction indicator. 



Resorcin Blue (CI, 908) — fluorescent blue, 

 iris blue — Often called Lacmoid. See 

 Nebel, B. R., Stain Techn., 1931, 6, 

 27-29. 



Resorcin-Fuchsin, see Weigert's resorcin- 

 fuchsin method for elastic fibers. 



Respiratory System. This contains very 

 diversified structural components for 

 which no single technique or group of 

 techniques can be offered. But the 

 interpretation of the preparations de- 

 pends, as in all systems of the body, 

 on the age. A chapter by Macklin, C. 

 C. and M. T., in Cowdry 's Problem of 

 Ageing, Baltimore : Williams and Wil- 

 kins, 1942, 936 pp., gives the necessary 

 background and numerous hints and 

 references to technique. See Lungs, 

 Trachea, Nasal Passages and Nasal 

 Sinuses. 



Respiratory Tract Smears, see Papanicolaou 

 Techniques. 



Respirometry, see Capillary Respirometry. 



Restaining Faded Sections. This is some- 

 times very desirable. Try technique 

 outlined by Small, C. S., (Amer. J. Clin. 

 Path., Techn. Suppl., 1943, 7, 66-67). 



Reticular Fibers. These are more finely 

 divided and tend more to form a reticu- 

 lum than the collagenic fibers. Yet 

 there may be anatomical continuity be- 

 tween collagenic and reticular fibers and 

 there is reason to believe that the two 

 are fundamentally similar. They are 

 not so conveniently viewed in the fresh 

 condition because to make thin spreads 

 is more difficult. For details see 

 Maximow, A. A., von Mollendorf's 

 Handbuch der Mikroskopischen Anato- 

 mic des Menschen, 1927, 2 (1), 232-583. 

 The principal methods for reticular 

 fibers in sections involve silver impreg- 

 nation (Perdrau, Foot, Wilder, Gomori 

 and Laidlaw), the choice of which will 

 to some extent depend on the kind of 



