rods, or threads which vary in size, number, and distribution from cell 

 to cell (Figure 3-2 (a) and (b) ). They are most readily identified in the 

 living cell by their affinity for the vital dye. Janus green. In size, they 

 range from elongate objects of several micra in length down to the limit 

 of resolution of the light microscope. When sections through individual 

 mitochondria are viewed with the electron microscope, a general pattern 



Figure 3-2. Phase-Contrast Photomicrographs of Mitochondria in Living 

 Cells from Culture of (a) Fetus Kidney, and (b) Salamander Heart. (Fig. 

 (a), courtesy of Mr. C. G. Lefeber, Pasadena Foundation for Medical Re- 

 search. Fig. (b), from Maximow, A. A. and Bloom, W., 1957. "Textbook of 

 Histology," 7th ed., W. B. Saunders Company, Philadelphia, Fig. 1-4A, p. 4. 

 Courtesy of Mrs. L. Wang.) 



of structure is revealed regardless of the type of cell in which they are 

 found. Basically, the mitochondrion is bounded by a double osmiophilic 

 membrane, each layer of which measures approximately 40 A in thick- 

 ness (Figure 3-3 (a) and (b)). The double membrane encloses an 

 inner matrix of variable diameter which is less osmiophilic and electron- 

 dense. The outer membrane is separated from the inner one by a space 

 of some 70 A in width. The interior is subdivided into a series of com- 

 partments by a system of double membranes, called the cristae mito- 



STRUCTURE AND FUNCTION OF CYTOPLASMIC ORGANELLES / 27 



