Section III 

 CELLULAR STRUCTURE AND ACTIVITY 



CHAPTER 1 



Cell Constitution 



FRANCIS O. SCHMITT 



Classical cytology was concerned primarily 

 with the elvicidation of cell structure by 

 examination, with the light microscope, of 

 living cells and of fixed and stained prepara- 

 tions. In the study of chromosomes, cytology 

 helped provide the foundation of modern 

 genetics by revealing a correlation between 

 chromosome structure and genetic function. 

 Histology has been of immense value in 

 physiology and pathology but in a more 

 limited sense. The limitations are primarily 

 (1) that the fundamental physiological ap- 

 paratus of the cell has dimensions far below 

 the resolving power of the light microscope, 

 and (2) that little is known concerning the 

 chemical composition and biochemical prop- 

 erties of the cell entities which can be op- 

 tically resolved. 



The development of new optical techniques 

 such as electron microscopy and various 

 cytochemical techniques, particularly the iso- 

 lation and characterization of cell particu- 

 lates, has enormously broadened the cytolog- 

 ical horizon. One has only to examine current 

 texts on experimental cytology, such as the 

 excellent compilation of Bourne ('51), to 

 see how important the biophysical and bio- 

 chemical aspects have become. Indeed, an 

 impressive portion of the work in analytical 

 cytology is now being done by general physi- 

 ologists, biochemists, enzymologists and bio- 

 physicists. 



This rapid expansion of experimental cy- 

 tology makes it impossible, within the space 

 of this chapter, to deal with the details of 

 cell constitution. Rather, we shall attempt to 

 outline the more salient features of cell 

 structure as they relate to function, particu- 

 larly in growth and development. Nuclear 



structures and nucleus-cytoplasm relations 

 will be considered in another chapter and 

 will therefore not be included in this presen- 

 tation. Where possible, key references will 

 be cited from which more detailed informa- 

 tion may be obtained. 



TECHNIQUES OF ANALYTICAL CYTOLOGY 



Most of the techniques of analytical cy- 

 tology are physical or chemical in nature. 

 The investigator in almost any field of 

 modern experimental biology should have a 

 general notion not only of the existence and 

 potentialities of these techniques but of their 

 limitations as well. Those wishing to employ 

 any of the various techniques effectively as a 

 fundamental portion of their research pro- 

 gram must understand that is it not enough 

 to learn the mere manipulations necessary 

 to "make the gadget work"; it is essential to 

 gain a good grasp of the physical and chem- 

 ical principles underlying the techniques. 



For the convenience of beginners in this 

 field, the principal techniques are listed, to- 

 gether with references from which an in- 

 troduction may be obtained. 



STRUCTURE ANALYSIS 

 (DIRECT METHODS) 



Ultraviolet and Infrared Microscopy and 

 Microabsorption Spectroscopy. Permit resolu- 

 tion higher than the light microscope. Give 

 information about chemical composition of 

 regions as small as 1 sq. /a in cells. References: 

 Caspersson ('50), Loofbourow ('50), Barer 

 et al. ('50). 



Electron Microscopy (EM). Provides resolu- 



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