102 Edward W. Dempsey 



studied in our laboratory by Dr. Jeffrey D. Lever. In the 

 outer portion of the fasciculata, mitochondria are numerous 

 and closely packed, they frequently have bizarre shapes and 

 are closely associated with a system of membrane-lined 

 vacuoles or tubules. Their internal structure differs from that 

 exhibited elsewhere; the internal membranes here are tubular 

 rather than laminar in configuration. The density of the 

 mitochondrial matrix varies greatly, some mitochondria 

 being excessively osmiophilic. In the zona reticularis the cells 

 are smaller and the mitochondria are less closely packed; 

 thus, it appears that with exhaustion of the cells, there is a 

 loss of mitochondria. 



Upon stimulation of the gland by exposure to cold or 

 by administration of adrenocorticotrophic hormone, the 

 mitochondria initially become less osmiophilic and their 

 membranous structures become more sharply evident. More 

 prolonged stimulation results in a restoration of the original 

 osmiophilia. In prolonged stimulation, bizarre forms become 

 more common and their structural alterations are more 

 extreme. The limiting membranes are frequently re-dupli- 

 cated and the internal folds become more complex. "Open" 

 forms have been encountered in which the internum of the 

 mitochondrion is continuous with the cytoplasm through 

 pores in its limiting membranes. 



These observations in various tissues and in different 

 physiological states suggest that mitochondria are labile 

 organelles, easily altered by changes in their physical environ- 

 ments. The experiments on vital staining show that the 

 inclusion within cells of foreign agents is of considerable 

 consequence to the integrity of their mitochondria. Ageing 

 and moribund cells, exemplified by the yolk-sac and the zona 

 reticularis of the adrenal gland, contain fewer and degenerat- 

 ing mitochondria. The experimental changes induced in 

 mitochondria in the secretory zones of the adrenal gland 

 offer hope, with further study, of understanding the manner 

 in which they are formed and their relation to secretory 

 processes. 



