THE ENDOCRINE ORGANS, OR DUCTLESS GLANDS 771 



often called chromaffin cells. There are also some cells containing coarser 

 granules that are soluble in water and do not stain with chrome salts. 



Embryologically, the medulla is developed from tissue common to it and the sym- 

 pathetic nervous system. From that part of the neuroblast in which are laid down the 

 primitive ganglia of the posterior roots, masses of cells are split off which become the 

 common ancestors of the sympathetic ganglia and the chromaffine system. These cell 

 groups wander from their sites of origin and come to lie along the vertebral bodies, 

 ranging themselves, in the case of the abdomen, on either side of the aorta. One mass 

 seeks the adrenal cortex, which has been formed at a prior stage of development, and 

 passes into its interior. Differentiation of these cells then proceeds in two directions, 

 those lying along the aorta form, for the most part, sympathetic ganglia; those within 

 the adrenal cortex develop into chromaffin cells to constitute the medulla of the gland. 

 These embryological considerations will enable us to understand the close functional re- 

 lationship which, as we shall see, exists between the sympathetic nervous system and the 

 adrenal medulla. 



The intimate anatomical association of the cortex and medulla renders 

 the removal of one part alone, if not an actual impossibility, a procedure 

 at least, of extreme difficulty. On this account, with the exception of the 

 investigations cited above, attention has been paid only to the effects pro- 

 duced by removal, or by the injection of extracts of the whole gland. 



Adrenalectomy 



Excision of the adrenal gland in most animals is very quickly fatal, 

 the only well-known exception being in the case of the white rat, in which 

 excision of both adrenals may not be incompatible with life. For some 

 time after recovery from the anesthetic the animal upon which double 

 adrenalectomy has been performed usually behaves in a perfectly normal 

 fashion, although it may be less lively and less inclined to feed than 

 usual. Very soon, however, generally within twenty-four or forty- 

 eight hours, definite symptoms of muscular weakness are apparent. This 

 weakness soon becomes extreme, and is accompanied by a feeble pulse, 

 a depression of body temperature, and, later, by dyspnea. After an 

 interval which is never longer than a few days, death supervenes, being 

 sometimes preceded by convulsions. 



When only one adrenal is removed, very few animals succumb; and 

 if some time is allowed to elapse so that the immediate shock of the 

 operation has disappeared, it will usually be found that removal of the 

 remaining adrenal, although ultimately fatal, is not so quickly so as 

 when both glands are removed at one operation. The reason for this 

 result is that opportunity is given for a compensatory hypertrophy of 

 accessory adrenal bodies to occur. Such accessory adrenal bodies may 

 be composed of cortical or medullary tissue, and there is a growing belief 

 that the cortical tissue is the more important. Chromaffin tissue is found 

 in most animals along the front of the aorta, between the renal arteries, 



