56 DEVELOPMENT OF CONNECTIVE-TISSUE FIBERS. 



MITOCHONDRIA AND THEIR RELATION TO THE CONNECTIVE 



TISSUE FIBRILS. 



One of the most convincing arguments in favor of the view that the fibrils 

 arise within the cytoplasm of the cells is the fact that frequently a few mitochon- 

 dria are seen along a primitive bundle of fibrils (plate 2, fig. 2) and that occasionally 

 a few are found isolated within a well-developed bundle of fibrils in the primitive 

 fiber (plate 2, fig. 3). So far as is known, mitochondria can not exist extracellularly. 



The mitochondria of the cells of the growth from a 6-day to 10-day chick 

 embryo are usually of several types; that is, the granular, the short-rod, and the 

 long-thread or filament type. The greatest number are filaments. Mitochondria 

 are scattered throughout the cytoplasm and occasionally along the network of 

 cell processes between the cells, and they may be arranged in a row along a cyto- 

 plasmic process (plate l,fig. 6). In a few instances a single filamentous mitochon- 

 drium has been observed to lie along the length of such a process (plate 2, fig. 3) . A 

 mitochondrium may be stretched along a fibril in such a way that in a fixed prep- 

 aration it would be difficult to determine whether or not it took part in the forma- 

 tion of the fiber. However, a study of the living cell shows that the mitochondria 

 retain all their characteristic activities. They continue to bend, twist, and 

 migrate, with the result that a mitochondrium, even though stretched for a time 

 along a fibril so that it appears to be part of the fibril, very soon bends and later 

 may move away. Mitochondria arranged in a row along a cell process do not 

 necessarily remain there, but may migrate into the body of the cell again. 



In the older cultures the cell processes are usually free from mitochondria. 

 In these cultures the mitochondria are more or less centralized around the nucleus 

 i. e., within the endoplasm of the cell. 



There is present in certain of the cells another structure, which stains in 

 the manner characteristic of mitochondria with the various mitochondria! stains- 

 red with Bensley's anilin-fuchsin methylene green stain (plate 2, fig. 7), black with 

 iron hematoxylin (plate 1, fig. 6), and purple with Benda's method. This structure 

 is in the form of a deposit along certain lines of the surface of the cell (plate 1, fig. 6), 

 and is not present in the cell in its early development, but appears later along the 

 edge or on the surface of the cell, and in certain cells, although not usually in those 

 of subcutaneous connective tissue, frequently seems to be associated with the for- 

 mation of fibrils. It seems probable that it is this structure rather than mitochondria 

 which Meves (1910) had under observation when he described the formation of the 

 fibrils of the tendon as taking place from the mitochondria after they had become 

 arranged along the surface of the cell. In the stained preparation this structure 

 definitely resembles the mitochondria, and it would be difficult to determine 

 whether mitochondria take part in its formation. However, the living cell shows 

 clearly that the structure is along the surface of the cell and that the mitochondria 

 do not take part in its formation. Also, while the structure is fixed and stained 

 by the same methods which fix and stain the mitochondria, it is not necessarily 

 destroyed by the agents which destroy mitochondria, but may be present in 



