LIPOID CONTENT OF THE KIDNEY TUBULE 77 
be reserved until the treatment of the ascending limb of the cat’s 
kidney, when its lipoid content is taken up. The transition 
between the distal convoluted and collecting tubules is gradual, 
and the clear type of epithelium characteristic of this portion 
needs no additional comment. 
OBSERVATIONS 
In this study of the lipoid content of the kidneys, cats were 
used more extensively, because the lipoids present were very 
easily demonstrated by fixers containing osmic acid. Definitely 
cut pieces of the kidneys from thirty-four cats were fixed in 
either Benda’s or Flemming’s fluids. All of these were found to 
contain lipoids that would reduce osmium tetroxid. Eleven of 
these cats were from 41 to 52 em. in length measuring from 
occipital crest to base of tail, fourteen were 30 to 38 cm., nine 
18 to 23 em.—that is, grown cats, half-grown cats, and small 
kittens. Of these, one died, four were killed by ether, and the 
rest by illuminating gas. The older full-grown cats had kidneys 
which were light in color and possibly pathological. Of the 
half-grown cats and kittens, only one pair of kidneys were found 
to be pathological upon gross examination, the rest appearing 
normal. Except for two kittens which had sore eyes, the external 
and internal appearances differed only in general thinness or 
fatness. Taking into consideration the above observations, one 
could almost always foretell how the section of kidney would 
look after it had been placed in Benda’s or Flemming’s fluid. A 
kidney of a very thin kitten or half-grown cat would have a 
cortex with very characteristic black rays; a fat kitten would 
possess a kidney, the cortex of which would blacken as a whole, 
while an old cat, fat or thin, would have a kidney with an intensely 
black cortex (figs. 1 to 8). In this gross examination of the 
kidney, the transition between the blackened cortex and lighter 
medulla was very evident as a distinct and clear-cut line. That 
the cat possesses fat different in amount, distribution, and com- 
position from other animals was evident in this very superficial 
examination, and may have some correlation with the obser- 
