CHAPTER 



QUANTITATIVE STUDIES 

 IN CYTOCHEMISTRY 



My own contribution to quantitative studies in cytochemistry 

 has been limited to pointing out some of the theoretical difficul- 

 ties in this field. The requirements of a system which will permit 

 quantitative studies are far from generally appreciated, and the 

 purpose of this chapter is to set out briefly the more general re- 

 quirements, so that the limitations of individual studies may be 

 more readily assessed. Since it is not practicable to give a de- 

 tailed account of all possible requirements in all possible situa- 

 tions, I shall limit the discussion to rather general problems, and 

 it should not be supposed that a study which complies with the 

 points to be set out is necessarily adequate. On the other hand, 

 any study which does not provide adequately for the solution of 

 all the problems which will be set out here is certainly inade- 

 quate. The problems which will be considered are the following: 



1. Errors due to scattering and refraction. 



2. Adherence to the Beer-Lambert law. 



3. Errors due to states of aggregation. 



4. Errors due to fixation and diffusion. 



5. Errors due to inadequate chemical procedures. 



6. Damage caused to specimen by illumination. 



Errors Due to Scattering and Refraction 



In almost all quantitative cytochemical studies, the experi- 

 mental procedure is to estimate the proportion of light which is 

 transmitted by the specimen at a variety of wavelengths. Since 

 cells are too small to permit such studies without magnification, 

 the experimental procedure involves examination of the distribu- 

 tion of light in a microscope image of the object, by means of 

 either a photographic method or some form of photocell. The 

 distribution of light in the image may be influenced by the 



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