IOWA ACADEMY OP SCIENCE 
215 
THE SOURCE OF THE CHROMAFFIN CELLS OP THE ADRENALS OP 
THE PIG. 
MILDKED YULE. ^ 
That the adrenals of mammals consist of cortical and medullary portions 
is well known, but there has been considerable diversity of views as to the 
source of these, especially as to the source of the medullary portion or the 
chromaffin substance. 
It is generally conceded that the anlagen of the adrenals arise in mammalian 
embryos as buds of cells which proliferate from the peritoneal epithelium. 
These push dorsally between the aorta and the wolflaan bodies to the position 
finally occupied by the mature gland. 
Early observers disagreed . in their conclusions as to the source of the 
chromaffin substance. As early as 1878 Balfour, working upon fishes, stated 
that its origin was from the sympathetic ganglia of the region. During the 
intervening time until 1901 its origin was variously ascribed to the mesenchyme, 
to the peritoneal epithelium, and to the epithelium of the pronephros. Later 
observers agree more closely. Wiesel (’01) working upon embryos of the pig 
too old to show the beginning of the adrenals concludes that the chromaffin 
substance is derived from the sympathetic plexuses. Whitehead (’03) agrees 
with this conclusion, his observations having been made upon younger embryos 
of the pig. Poll (’06) sums up the evidence in all classes of vertebrata as 
favoring the view that cells separated from the sympathetic nervous system 
give rise to the chromaffin substance of the adrenals. The work oLKuntz (’12) 
shows conclusively that in the turtle there can be no doubt as to the origin 
of the chromaffin substance from the sympathetic system. 
The following observations upon embryos of the pig were made by the 
writer during the past year. 
No cells destined to become chromaffin cells were seen in the adrenal buds 
until after the ^sympathetic matter had pushed ventrally below the level of 
the aorta, which position is also ventromesial and in close proximity to the 
adrenals. Embryos 6 mm in length show no sympathetic cells ventral to the 
middle level of the aorta while the adrenal buds are well formed. Small 
groups of sympathetic cells are seen dorso-laterally to the aorta, evidently 
moving toward the adrenal region. In embryos 12 mm. in length sympathetic 
cells have formed loose lines near the mesial surface of the wolffian bodies 
directed ventrally to the level of the adrenal buds where they swipg mesially 
and meet ventral to the aorta. The sympathetic matter in the region of the 
coeliac plexus in embryos 19 and 20 mm. in length has increased greatly in 
the number of cells and shows distinct fibres in the central region. Almost 
the entire mesial surface of the bud lies in contact with aggregates of sym- 
pathetic cells. Some of these cells have migrated laterally and envelop the 
