QUARTZ ROD TECHNIQUE 



296 



RADIOACTIVE ISOTOPES 



of physiologic or pathologic processes 

 and watch or otherwise determine the 

 responses of parts of living systems to 

 the newly arrived material. For an 

 extensive example of one such set of 

 studies, see Knisely, M. H., Bloch, 

 E. H., and Warner, L., cited above. 



5. The method permits the study of 

 some kinds of pathologic processes while 

 they are still in reversible stages, that 

 is, in controllable stages. Autopsies 

 and autopsy sections show the final 

 cumulative results of all of the simul- 

 taneous and consecutive pathologic and 

 reparative processes which had been 

 going on. That is, they show the pre- 

 servable, visible part of the accumu- 

 lated results after some one or more sets 

 of pathologic processes have become ir- 

 reversible. The microscopic studies of 

 living tissues allow examination of some 

 pathologic processes (a) as they de- 

 velop, (b) as they proceed at sublethal 

 degrees of intensity, and (c) as they 

 accumulate toward lethal combinations 

 of factors, but are still reversible, that 

 is while the animal's life can still be 

 saved, and (d) as they accumulate into 

 non-reversible stages. Further, the 

 method permits study of the results of 

 experimental therapeutics on visible 

 pathologic processes. For demonstra- 

 tions and elaboration of this theme see 

 Knisely, M. H., Stratman -Thomas, 

 W. K., Eliot, T. S., and Bloch, E. H., 

 1945, cited above. 



It may seem to some that the above 

 discussion is too critical or unjustly 

 critical of the histological sectioning 

 techniques, or that the author is trying 

 to laelittle their use. This I do not be- 

 lieve to be so. The best histologists 

 have always studied sections not for the 

 structure of the dead sections them- 

 selves, but rather to determine as closely 

 as possible the structure and functions 

 the tissues had had when last alive. Pre- 

 cision and accurac}'^ in developing con- 

 cepts from the evidences gathered by a 

 technique can never be greater than the 

 user's understanding of the inherent 

 limitations of that technique. The ac- 

 curacy of a technique cannot be deter- 

 mined simply by repeating its steps an 

 infinite number of times; its limitations 

 and degrees of accuracy must also be 

 cross-checked by other and, if possible, 

 quite different techniques. Each useful 

 technique delineates one or more aspects 

 of the original tissue more accurately 

 than do other techniques. Obviously 

 the most accurate and comprehensive 

 concepts of micro-anatomy, microscopic 

 physiology and microscopic pathologic 

 physiology can be developed only by 

 synthesis; by putting together in the 



mind of the student the most accurate 

 of the available individual aspects. For 

 this purpose each technique has special 

 values of its own; for this purpose not 

 enough different techniques are yet 

 available. 



Quinoline Dyes. Only pinacyanol is of ap- 

 parent value to histologists. 



Quinone-Imine Dyes. Possess 2 chromo- 

 phores : indamin-N= and quinoid ben- 

 zene ring. They are divisible into 

 Azins, Indamins, Indophenols, Ox- 

 azins, Thiazins. 



Quinone Oximes, see Nitroso Dyes. 



Rabbit Ears, see Sandison's Technique for 

 inserting transparent chambers in. 



Rabies, see Negri Bodies. 



Rabl's Fluid is sat. aq. mercuric chloride, 

 1 part; sat. aq. picric acid, 1 part; aq. 

 dest., 2 parts. 



Radiation. Methods and results of radia- 

 tion of normal tissues reviewed (Warren, 

 S. and Dunlap, C. E., Arch. Path., 

 1942, 34, 562-608 and earlier papers). 



Radioactive Isotopes— Written by T. B. 

 Rosenthal, Dept. of Anatomy, Washing- 

 ton Universit}-, St. Louis. June 6, 

 1951. — The release of radioactive iso- 

 topes in large quantities for civilian 

 use (1946) has resulted in a voluminous 

 literature concerned with fundamental 

 concepts of metabolism and with the 

 diagnosis and treatment of malignant 

 disease. Although only a few notable 

 discoveries may be directly attributed 

 to the use of these isotopes (since the 

 basic ideas were derived from earlier 

 work with stable isotopes and conven- 

 tional biochemical methods), it must 

 be admitted that the relative ease and 

 speed of operations with radioactive 

 isotopes have thrown open a hitherto 

 difficult field. By these means the 

 validity of many old concepts has been 

 confirmed, while others have been 

 conclusively demonstrated to be false. 

 It must be emphasized however that 

 research with isotopes has not dis- 

 placed the traditional methods in biol- 

 ogy and chemistry. Reliable tech- 

 niques are still requisite, and there is 

 more need for good analytical chemistry 

 than ever before. The radioactive iso- 

 tope now takes its proper place among 

 the resources of the laboratory as a tool 

 indispensable for certain problems, use- 

 ful for others, and merely optional for 

 still others. 



Mass production of reliable instru- 

 ments for measurement of radio-activ- 

 ity has extended the use of isotopes to 

 those laboratories previously deterred 

 by expense or lack of specially trained 

 personnel. The choice of equipment, 

 i.e., Geiger-MuUer counters, propor- 

 tional counters, scintillation counters, 



