CHOICE OF METHODS XXV 



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 vaUdity. 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 photometrically 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. 



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

 of the day and the limitations thereof cannot be envisaged. In this elementary 

 survey only a few others can be mentioned briefly in passing as examples. By 

 Electrophoresis measurements the electric charge on particles can be determined. 

 The Polarization Optical Method is of surpassing value and Fluorescence Micros- 

 copy, supplemented by fluorescence spectrography, is coming into its own. 

 Surface Tension measurements can be made in numerous ways. Particle 

 size can be measured by a flock of different techniques from which the one must 

 be chosen that best suits the material. The simplest way is to compare the 

 objects with rulings of a micrometer slide. DiflTraction methods are labor saving 

 and often preferable. Filters of d^erent porosity are available so that the 

 sizes of particles passing through can be roughly gaged. To employ Ultra- 

 centrifugation techniques are among several other possibilities. There are 

 now Microscopes of many varieties to choose from. 



The Electron Microscope is a physical tool which can be used only by a spe- 

 cially trained individual, and it has the limitation that the cells and other ma- 

 terials must be very thin, sections not more than about j of a micron. See 

 Burton, E. F. and Kohl, W. H., The Electron Microscope. New York: Rein- 

 hold Publishing Corporation, 1946, 325 pp. 



In biology and medicine it is clearly evident that the techniques of physics 

 and chemistry are so revealing that some knowledge of these basic sciences is 

 necessary. A little knowledge can however be a dangerous thing often leading 

 to half baked conclusions. Cooperation with real physicists and chemists is 

 essential and team work must take the place of isolated individual endeavor, 

 moreover a laboratory of whatever kind must be well organized to be effective. 



