78 CHRISTIANNA SMITH 
vations of Mottram (716) in regard to the saturation of the fats 
present in the cat’s kidney. 
As a typical example of a kidney whose cortex is characterized 
by blackened rays, one will be studied from a 22-cm. kitten 
which was guite thin. The kitten was killed by gas and its 
tissue fixed immediately. The kidney appeared normal and 
healthy. As the appearance of lipoids depends upon its preser- 
vation and staining, the lipoid content will be examined in its 
relation to the methods used. 
Ten per cent formalin and scarlet red. Free-hand sections 
were made from material that had been in 10 per cent formalin 
for about a week, and stained with an alkaline alcoholic solution 
of scarlet red (Bullard, 71213). Formalin material was used 
in this case because the lipoids of the kidney of cat are little 
affected by it. The rayed appearance of the cortex noted in 
the gross examination of tissue fixed in Benda’s was apparent 
here, and the rays proved to be composed of tubules containing 
heavily stained lipoid granules in the medullary rays. The 
tubules of the labyrinth and medulla also contained granules, 
but they were much finer than those in the rays. 
Potassium bichromate and sudan III. This method was first 
used by Bell, who said it would stain all granules seen in a fresh 
specimen and would also differentiate those containing olein 
from other lipoids. The medullary rays which were stained 
with Benda’s or scarlet red, thereby standing out prominently 
because of their intense staining, were here very light in color, 
and the tubules of the labyrinth were darker. This variation 
was due to the fact that those granules which were deeply stained 
by scarlet red or Benda’s were stained only at the periphery or 
not at all with sudan III after chromation. These droplets, 
then, could be said to contain olein because they reduce osmic 
acid and because they were chromated on the surface or not at 
all by Bell’s method, or are what he called annular droplets. 
The medulla was also divided into two regions, one, corresponding 
to the outer zone of Peter, which lies next to the cortex, con- 
tained more deeply staining tubules than the inner zone or 
papilla. 
