452 



COMPARATIVE ANATOMY 



Histology. An adrenal has two kinds of tissue, an outer yellowish 

 cortex and an inner brownish medulla. The cortex is subdivided into 

 three layers, an outer glomerular layer composed of rounded clusters of 

 epithelial cells, a middle fasciculate layer of rounded cells arranged in 

 cords perpendicular to the surface, and an innermost reticular layer in 

 which the cellular cords unite in a network. The central or medullary 

 portion of the adrenal is characterized by relatively large "chromaffin" 

 cells, so-called because they have a strong affinity for chromic salts, which 



■ZONA FASCtCUUVTA. 



Fig. 377. — A portion of a section of the adrenal gland as seen under low power 

 microscope, showing the differentiation into cortical and medullary regions. Different 

 endocrines are secreted by these two tissues, which have a different embryonic origin. 



Stain them brown. They are arranged in clusters separated by numerous 

 lacunar blood spaces. A compact connective tissue capsule encloses the 

 glandular tissues. (Figs. 377, 378) 



Physiology. The adrenals have a double function corresponding with 

 their histological differentiation into two tissues. The cortex secretes an 

 endocrine, cortin, of unknown chemical composition, which is essential 

 to life. Destruction of the cortex by tuberculosis or tumor is followed 

 by Addison's disease, which is characterized by a deep pigmentation of the 

 skin and great weakness. Death comes rapidly unless cortin is adminis- 

 tered. The effect of cortin is, however, immediate, and the patient 

 suffering from adrenal failure promptly arises as though from the dead. 



The cortex of the adrenal is, relatively to the medulla, largest during 

 foetal life, and there is little doubt that its secretions have a strong influ- 

 ence upon growth. Excessive activity of the gland induces precocious 

 development. The stages of life are so speeded up that a child of four 

 or five may look like an old person. Hyperactivity of the cortex also 



