2 

 THE INTERPHASE CELL AND THE CYTOPLASM 



In this chapter will be described the appearance and structure of one 

 particular type of cell ; the nature and composition of its component 

 structures will be discussed with reference to other cells for which 

 evidence is available. A flattened 'fibroblast' in the outgrowth of a 

 culture of skeletal or connective tissue of a chick or mammal will serve 

 as a representative type of cell for our purpose. Such living cells in the 

 outgrowth of cultures photographed by phase-contrast are illustrated 

 in Plate L The fibroblasts from cultures of bone should be more 

 strictly called osteoblasts for under appropriate conditions in culture 

 they may again take part in the formation of bone in the outgrowth of 

 the culture. From a number of explanted tissues, cells of the general 

 fibroblastic form will grow out in a partially de-differentiated condi- 

 tion; they are then not necessarily identical, for differences in the 

 metabolism between races of such cells have been demonstrated 

 (Parker^). Thus the word fibroblast is used loosely, and as Willmer^ 

 says : 'The use of this term arose not because the cells necessarily have 

 any connection with the formation of fibres, although some of them 

 may show this property, but because they are similar in appearance to 

 the cells in the body which are beheved to function in this manner.' 



CYTOPLASMIC INCLUSIONS 



The cytoplasmic structure of such cells in tissue culture has been 

 studied many times. Among studies of this kind are those of Lewis and 

 Lewis,3 Strangeways and Canti,* and Ludford.^ Claude et alii^ ' 

 have reported on the electron micrography of cells in tissue culture, 

 while observations with the phase microscope are described by Zollin- 

 gerS and Hughes. ^ Richardson^^ and Hill" have been specially 

 concerned with the Golgi body. All are agreed that the cytoplasm 

 contains granular or filamentous mitochondria and also granules and 

 vacuoles. As with other cells, the existence and the nature of the Golgi 

 body has been disputed, and not all authors mention whether a central 

 body is to be observed. Since tissue culture fibroblasts include several 

 sorts and conditions of cells, it is not remarkable that descriptions of 

 them can differ in detail. The inclusions are set in an apparently clear 

 and homogeneous cytoplasm, seen best at the margin of the cell, near 

 which the mitochondria are seen most distinctly (Plate I (i)). Further 



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