LIPOID CONTENT OF THE KIDNEY TUBULE 79 
When the cortex was examined more closely, it was found that 
the cells of the proximal convoluted tubule which had stained 
deeply, contained a large number of lipoid granules, some portions 
of the tubules more than others. As stated by Bell, when there 
was a small amount of lipoid present, the granules were collected 
at the base of the cell, and when a large amount was present, 
the granules were scattered through the cell. Where the lipoid 
was stained, the mitochondrial filaments stood out among them 
in contrast very clearly. Although there was a tendency for 
one tubule to have the same kind of droplets, it was very common 
to find in the same tubule both annular and solid forms. In 
some sections of annular droplets, a diffusion of the lipoid into 
the surrounding cytoplasm could be seen quite plainly. It was 
also noted that many irregular-shaped granules seemed to be 
composed of two or more droplets. 
The tubules containing the very large droplets which stained 
intensely with osmic acid and scarlet red, and not at all or very 
little with sudan III, were the medullary segments of the 
proximal convoluted tubule. Although Bell describes the type 
of droplets which contains olein as annular, from observations 
on both normal and pathological kidneys where droplets which 
‘stained intensely black were very abundant, it would be seen 
that the larger droplets were not preserved at all and represented 
vacuoles. That this condition was not due to sections where 
the fixation was incomplete was shown by the fact that neighbor- 
ing proximal convoluted tubules possessed lipoid which stained 
with sudan III (fig. 12). 
The transition from the medullary segments of the proximal 
convoluted tubule to the descending limb was very sharp and 
the cause of the clear-cut line apparently between the cortex and 
the medulla which was noticed in the gross examination. The 
pavement epithelial cells of this part of the medullary loop or 
the loop of Henle possessed solid lipoid granules, quite numerous 
and large in proportion to the amount of cytoplasm in the cells. 
The ascending limb of the loop had an appearance very different 
from the other portions of the renal tubule because of the presence 
of the rods which Policard describes (’05, 10, 12, 713). Although 
THE AMERICAN JOURNAL OF ANATOMY, VOL. 27, NO. 1 
