262 THE ENDOCRINE GLANDS 



and cells degenerating there migrate into the reticularis, where 

 they are removed by macrophages. 



The M edulla . ^This region consists of an irregularly arranged 

 meshwork of polyhedral cells separated by sinusoidal capillaries. 

 The medulla cells are also roughly rectangular in section, with the 

 longer sides in contact with adjacent cells and with a sinusoidal 

 capillary adjacent to the short sides. When fixed in chromic acid 

 the cytoplasm of the cells is dark brown in color, and if potassium 

 dichromate is used their cytoplasm shows fine brown granules. 

 Because of this affinity for chromium they are referred to as chromaf- 

 fin cells. In ferric chloride the medulla stains green and in iodine 

 yellow. The fine brown granules are secretory products which 

 reduce dichromate of potassium to chromium dioxide. The number 

 of granules present indicates the degree of secretory acti^^ity. 



There is a plexus of fine nerve fibers in the cortex, especially in the 

 zona reticularis. Axons of nerve cells are in close relation with the 

 chromaffin cells of the medulla. Here also are a few ganglion cells, 

 or even small ganglia near the central vein. Since the medulla is 

 derived from the same source as the sympathetic nervous system, 

 this central portion of the adrenal is comparable to paraganglia 

 to be described presently. Secretion of the cortical and medullary 

 portions appear to have dift'erent functional effects. The cortex is 

 said to produce a special hormone, now called "cortin." Lack of 

 cortin in man, due to ]:)athological lesions of the cortex, results in 

 Addison's disease. Animals deprived of adrenals die, but life is 

 prolonged if extract of cortical tissue is administered. 



Epinephrin, or adrenalin, or adrenin, is secreted by cells of the 

 medulla. Circulating in the blood stream, it maintains tone in 

 the small arteries, or arterioles, and so assists in regulating blood- 

 pressure. Local injections of adrenalin cause temporary constric- 

 tion in small ^'essels, and in this manner it is used for preventing 

 hemorrhage. Lijections of it into a heart that has ceased beating 

 for a short period in some cases results in a resum])tion of rhythmical 

 contractions. 



THE CAROTID GLANDS. 



There is a small mass of glandular tissue similar to that of the 

 adrenal medulla at the forking of each carotid artery into its external 

 and internal branch. This mass, known as the carotid gland, has 

 a connective-tissue sheath enclosing a mass of epithelioitl cells well 

 supplied with a ca])illary network. Small sympathetic ganglia are 

 associated with these glands, and the resemblance of the glandular 



