128 INTERNAL SECRETION 



another both in colour and consistency. This difference was 

 recognized by the earlier investigators, by whom the two portions 

 were distinguished as the " medulla " and the " cortex." These 

 terms are not merely topographical, but possess a histological 

 significance. The microscopic examination of the more minute 

 structure shows that the medulla and the cortex of the suprarenals 

 are composed of two different tissue formations. 



The cortex is composed of rows and columns of cells contain- 

 ing a varying quantity of shining granules, which are partly 

 double-refractive. The characteristic reactions of these granules 

 show that they contain fat or are closely related to lecithin, and 

 for this reason they are known as lipoid granules. They colour 

 strongly with the specific analine dyes for fats (alkanet, sudan III, 

 scarlet R.); they stain black with fluids containing osmium; and 

 they are more readily soluble than fats in fat-dissolving agents 

 (chloroform, xylol, ethereal oils). 



The medulla consists of a tissue well furnished with nerves 

 and vessels, and composed of spheroid or cord-like cell-agglomera- 

 tions, the cells of which possess a specific affinity for chromium 

 salts. The contents of these cells are very evanescent, but they 

 may be preserved in chromic acid and solutions of the chromic 

 acid salts, by which they are coloured a light yellow to dark brown 

 (Henle, 1865). The finely granular cyptoplasm has a marked 

 affinity for the specific stains for nuclei (carmine, hasmatoxylin, 

 safranin) and colours a black-green with ferric chloride. 



Thus, the anatomically homogeneous suprarenals consist his- 

 tologically of a peculiar combination of two different tissues, the 

 cells of one being characterized by their lipoid contents and those 

 of the other by their chromaffinity. 



This differentiation is not sufficient, however, when we come 

 to the anatomical comparison of the homologous organs of the 

 different classes of animals. It is only in the higher mammals 

 that well-defined paired organs are met with which, from their 

 position and partly also from their structure, can be identified as 

 suprarenals. In birds these organs consist of the two characteristic 

 kinds of tissue, but the topographical arrangement of medulla and 

 cortex is absent. It is rather the intimate interweaving of two 

 nets of cell-columns of which one the system of principal 

 columns has all the histological characteristics of the suprarenal 

 cortex, the other the intermediary system presents those of the 

 chromaffine medulla. The conditions in reptiles are essentially 

 the same, but it is worth noting that here the tissue with lipoid 

 cell-contents is largely predominant; it is only in the hydro- 

 sauria and chelonia (crocodile and tortoise) that these cortical ' 

 threads are interwoven with fine medullary threads. In the lepido- 

 sauria (lizards and snakes), isolated balls of medullary substance 

 are scattered in a ventral direction in the cortex, and the greater 

 part of the chromaffine tissue occupies a dorsal position. 



