CHAPTER II 



PRELIMINARY DESCRIPTION OF THE CELL 



In a survey of the evolution of biological science it is noticeable that, 

 while diverging lines of inquiry have broadened the field of view, the 

 attention of investigators, speaking generally, has been directed in turn 

 to successively smaller constituent parts of the organism. For many 

 years plants and animals were studied chiefly as wholes. But very 

 early there were made many scattered observations on the various or- 

 gans and tissues composing the body, and from these relatively crude 

 beginnings morphology and histology later arose. Again, when the 

 protoplasmic mass which we know as the cell came to be recognized as 

 the unit of structure and of function, it was evident that the problems 

 it presents should be investigated to a certain extent by themselves, and 

 such investigation is the task of modern cytology. 



Within the field of cytology itself the focus of attention has gradu- 

 ally shortened. While many workers occupied themselves with a study 

 of the general behavior of the cell nucleus, others devoted their efforts 

 entirely to an investigation of its important constituent elements, the 

 chromosomes. Furthermore, cytologists at present are much interested 

 in knowing whether or not any smaller units, corresponding to the 

 "genes" of the geneticist, can be directly demonstrated, and whether 

 or not the chromatic granules or " chromomeres " are of significance in 

 this respect. 



In the course of all such studies there are encountered questions 

 which must be referred ultimately to the chemical molecules and atoms 

 and their interactions within the cell, so that biochemistry may in a 

 measure be looked upon as a department of cytology, just as it is to be 

 regarded in other respects as a subdivision of chemistry. The subject of 

 cytology thus occupies an important position in the system of natural 

 sciences. It stands with chemistry and physics on the one hand and the 

 complex phenomena peculiar to living organisms on the other; and the 

 steady mutual approach of the physico-chemical and biological fields 

 is due in large measure to the results of morphological and physiological 

 studies on the cell. 



For the term cell we are indebted to Robert Hooke and the other 

 microscopists of the seventeenth century, who applied it to the small 

 cavities in the honeycomb-like structure which they discovered in plant 

 tissues. Today the term denotes primarily the protoplasmic "cell 

 contents," which, strangely enough, the early workers regarded as an 



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