10 CHOICE OF METHODS 



ponents in the positions they occupy in the living state is to instantaneously 

 freeze the tissue and dehydrate in vacuum while still frozen, thus avoiding all 

 fixatives, by the Altniann-Gersh technique. Moreover, the reagents used in 

 testing must contact all the tissue equally for unequal contact may well be 

 followed by stronger reactions in some areas than in others. 



Quite recently chemical analysis has been accurately focussed, not merely 

 on cells, but on fiarts of cells. Nuclei, Mitochondria and many other cellular 

 components including even Chromatin Threads can now be collected en masse 

 by Centrifugation of broken up cells and analysed. This is a departure of con- 

 sequence. 



Finally standard qualitative chemical methods are often applicable on a 

 microscopic basis. The reader wishing to do so may well consult Chamot, E. 

 E., and Mason, C. W., Handbook of Chemical Microscopy. New York: John 

 Wiley & Sons, 1940, vol. 2, 439 pp. Another book that will be found of service, 

 especially for analysis on microscopic slides, is Benedetti-Pichler, A. A., In- 

 troduction to the Microtechnique of Inorganic Analysis. New York: John 

 Wiley & Sons, 1942, 302 pp. Sometimes one is held up by having to deal with 

 some unfamiliar chemical substance in which case aid may be secured from the 

 large and comprehensive "Dictionary of Organic Compounds" edited by Heil- 

 bron and published in 3 volumes, 1934, 1936 and 1938, by Oxford University 

 Press, New York. No attempt is made in this dictionary to include dyes but 

 thousands of other organic compounds are conveniently arranged in alphabetical 

 order. If the wanted material is some sort of medical preparation seek infonna- 

 tion in the following reference books. (1) New and Nonofficial Remedies, 

 1946. Chicago: Am. Med. Assoc, 770 pp.; (2) The National Formulary. 

 VII. Washington: Am. Pharmaceutical Assoc, 1942, 690 pp.; (3) The Phar- 

 macopoeia of the U. S. XII. Easton: Mack Printing Co., 1942, 880 pp. 



8. To Employ Physical Techniques in the Investigation 



OF Composition 



Chemistry is, at rock bottom physics so that the distinction here made is 

 convenient but without validity. Hydrogen Ion Indicators and Oxidation- 

 Reduction Potential could come under either heading. 



Histospectrography is a quick and reliable method to gain information on 

 the presence or absence of many minerals. It is a kind of survey technique, 

 for the absorption lines of many elements can be obtained in a single spectrogram. 

 The density of the lines can be determined photometricalh^ but data obtained on 

 concentration of a particular element are relative (more in one tissue than in 

 another) but not absolute (in mgm. per gm. of tissue). Ultraviolet Absorption 

 Spectra have been employed to advantage by Caspersson and others in the 

 intracellular determination of certain components but the technique requires 

 elaborate and costly instrumentation. It gives promise, however, of being 

 of great value in the solution of fundamental problems. 



UtiUzation of physical techniques in biology and medicine is now the order 



