CELLS AND TISSUES 



physical and chemical states of protoplasm and its differentiations in 

 cells, as well as to correct many misconceptions due to inference from the 

 aspects presented by fixed material. Of great interest also is the recent 

 application of motion-picture photography to cytological problems. 

 Films taken slowly of cells in tissue cultures and then projected at high 

 speed have served to furnish information, especially with respect to time 

 relations, which it would be difficult or impossible to obtain by any other 

 means. Moreover, they have placed desirable emphasis on the concep- 

 tion of the cell as a dynamic system. As a consequence of the renewed 

 study of living cells, it has been possible to evaluate anew the results 

 obtained by the standard methods of fixation and staining and to improve 

 upon such procedures. Critical studies have been made upon cells 



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Fig. 3. — Spermatocytes of Stenobothrus (Chorthippus) lineatus: (1) living; (2) after 

 treatment with OsOi vapor and Flemming's fixing fluid; (3) after staining and mounting. 

 {After Belar, 19286.) 



i 



before, during, and after fixation and staining^ (Fig. 3) ; and as a result 

 it appears that, although the cytologist must be on his guard in inter- 

 preting the finer details even in his best fixed preparations, the general 

 picture presented in such material is on the whole strikingly true to 

 nature. Moreover, it is abundantly evident that no single set of methods 

 will suffice to solve all of cytology's problems. 



Development. — In studying the development of any small, relatively 

 undifferentiated mass of nucleated protoplasm into a mature organism 

 and in interpreting the role of cells and tissues in this process, there are 

 certain general phenomena which may be considered before taking up the 

 more special data of cytology. These are growth, morphallaxis, differ- 

 entiation, and correlation. 



By groxDth is meant primarily the synthesis of new protoplasm through 

 the activity of the old, and secondarily the increase in body size which 

 usually results. The synthetic processes involve an extensive interchange 



« See Martens (19276c) and Belaf (1929a). 



