The Comparative Histology of the Suprarenal Capsules. 309 



There has been a considerable amount of confusion as to the form 

 of the cells of the mammalian medulla. They have frequently been 

 described as irregular in form, as having processes, and as leaving 

 irregular spaces between individual cells. These appearances are figured 

 by Eberth [30, 31] and his drawing has been extensively copied into 

 the text-books, but I am convinced that it is fallacious. It is certain 

 that after some methods of preparation these appearances are seen. 

 Thus, the arrangement seen in PI. XVIII. fig. 16 is often obtained. 

 But I am persuaded from the study of several species and the em- 

 ployment of many different modes of fixing and hardening, that this 

 appearance does not represent the true structure. I was at first of 

 the opposite opinion because the appearances so much resemble the 

 homologous structure in Elasmobranch fishes (cf. PI. XVI. fig. 1 and 

 PI. XVIII. fig. 3 with PI. XVIII. fig. 16). The peculiarity seen in 

 these cases I attribute to two causes [1] shrinkage from the employ- 

 ment of bichromate of potassium [2] a softer and more delicate structure 

 of the medullary cells, which causes them to break up under the razor. 



When alcohol or formol is employed as a fixing agent, one always 

 gets appearances closely resembling those depicted in PI. XVII. fig. 15, 

 which represents a small portion of the medullary substance of the sheep. 

 Here the medulla has the general arrangement described above, which 

 I believe to be the typical one, and the cells are regular in form. Even 

 after hardening in Müllers fluid, if care be taken in the preliminary 

 processes and in the cutting of the sections, one frequently gets the 

 cells regularly disposed in close contact with one another as in glands 

 generally, and with no signs of shrinkage of the individual cells. 



The general arrangement of the medullary cell-columns does not 

 differ very much in the different species of mammals which I have 

 studied. In man, the cat, the dog, and some others, the appearance 

 is almost precisely like that drawn in PI. XVII. fig. 15 for the sheep. 



V. Brunn [13] finds smooth muscular fibres in the medullary 

 substance in man, and in much smaller numbers in the horse, rabbit 

 and cat, but states that they are absent in most animals. They occur, 

 according to this observer, round the great veins in the medullary 

 portion of the gland, and are longitudinal in direction only, no cii'cular 



