CHOICE OF METHODS 11 



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. Dififraction methods are labor saving 

 and often preferable. Filters of djifferent porosity are available so that the 

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

 centrifugation techniques are among several other possibilities. There are 

 now Microscopes of manj^ 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 ^ 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 knoAvledge 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. 

 An untidy laboratory is not a sign of industry but an indicator of carelessness, 

 and sometimes a source of actual danger to the occupants. 



9. To Detect Deviations from Normal 



The Normality of a tissue or organ is often in doubt. There is no single 

 technique capable of yielding an unqualified answer. Since some properties 

 may be normal while others are abnormal (pathological) we need first to be told 

 the property under consideration. If it is, for instance, the amount of contained 

 pigment, this can be said to be normal when it is the amount usually present in 

 a particular tissue under the same conditions. By the word "usually" is in- 

 tended in the majority of cases, that is in 51 per cent or in any higher percentage. 

 The phrase "same conditions" means that the conditions likely to influence the 

 amount of pigment are so nearlj' alike as to be not responsible for any difference 

 observed between the property of the tissue where normality is in question and 

 that of others of the same kind. Thus, we could say with reasonable assurance 

 that the amount of pigment is normal if it is that usually demonstrated by the 

 same technique in tissues of the same kind of animals of the same species, sex 

 and age living under the same conditions. Judgment is necessary in specifica- 

 tion of possibly modifying conditions which mil depend to some extent on the 

 propert}'^ under consideration and on the number of observations necessary to 



