HISTOLOGY 47 



to the unequal staining of two types of cells which have been 

 described as dark and light cells. The former are large rounded 

 cells, with a finely granular pale-staining cytoplasm and con- 

 tain few mitochondria, little lipid, and little pigment. The 

 latter stain deeply, have a hyperchromatic or pyknotic nucleus 

 and abundant mitochondria, lipid, and pigment. 301 The rabbit 

 possesses no reticularis, the fasciculate cells being contiguous 

 with the medulla. In the mouse, likewise (Figure 9) no clearly 

 defined zona reticularis is distinguishable but in the other ro- 

 dents (Figure 4) the inner part of the cortex is characterized 

 by an irregular or reticulate arrangement. 



In man at birth there is a large zone between the reticularis 

 and the medulla. This zone undergoes involution during the 

 first year of life and is replaced by a very thin "juxta-medul- 

 lary" zone. 231 Both of these zones, as well as their homologues 

 in other animals, shall be described in the next chapter. 



The cells of the adrenal cortex in almost all animals are 

 characterized by the presence of large amounts of lipids, the 

 nature and significance of which shall be discussed in Chapter 

 XX. The most frequent point of deposition of this lipid is in 

 the fascicularis. However, in the armadillo (Dasypus septem- 

 cinctus) the lipid is found in the glomerulosa. In the cat also 

 this zone contains fatty inclusions. In the rabbit, guinea pig, 

 elephant, bear, and rhinoceros, there is a deposition of much 

 lipid in the zona reticularis. The adrenals of certain Insecti- 

 vores (hedgehog, mole) and of the marmot (Arctomys marmot) 

 are relatively free of lipid as observed histologically, while in 

 a normal healthy specimen of the emu (Tragulus javanicus) 

 Kolmer 362 was unable to detect any lipid. This finding is of 

 particular interest since many authors have looked upon the 

 lipid as the specific secretion of the adrenals. 



The cytology of the cortical cells has been the subject of 

 frequent study in the hope of elucidating the function of the 

 adrenals. These glands offer a rich field for the microscopist, 

 but it is difficult to evaluate the significance of the results 



