LIPOID CONTENT OF THE KIDNEY TUBULE 87 
tained cells with granules which stained brown with 1 per cent 
osmic acid. 
Ten per cent potassium dichromate and sudan III. Unlike the 
kidney of the cat, the cortex did not possess any differentiation 
into rays, but, like it, possessed the two regions of the medulla, 
the outer zone staining more deeply. Granules were present in 
the cells of the proximal convoluted tubules which Bell called 
sudanophile precipitate, and for which he did not consider the 
evidence sufficient to consider as diffuse lipoids. According to 
Bell, sudanophile precipitate was not found in cells containing 
lipoid granules. As droplets were found in the tubules of the 
cortex which stained with scarlet red and browned with osmic 
acid, the conclusion was reached that the granules here were 
lipoids and not precipitates. The fatty nature of the rods in 
the ascending limbs of the medullary loops was evident although 
they stained very lightly. 
Benda’s fluid. Material, autolyzed or not, showed no fat 
which would reduce osmic acid when Benda’s fluid was used 
without the application of heat. Also, tissue which had not 
undergone autolysis, but was preserved in Benda’s fluid kept at 
a temperature of 51°, exhibited no blackened granules. Sections 
which had autolyzed and were fixed in the way just mentioned 
presented a quite different appearance. Many black granules, 
short granular filaments, and rods were present in the cells of 
the cortical tubules and in the interstitial tissue of the cortex 
and medulla. Therefore, from these observations it would seem 
that lipoids which reduce osmic acid are found in the kidney cells 
of the rabbit only after autolysis and fixation with heat. Ziegler, 
in his discussion of fatty degeneration (p. 199), says that “a 
process similar to that taking place within the body occurs 
during autolysis of tissue preserved aseptically in the incubator, 
fat droplets becoming visible in such tissues (Hensen, Wentcher, 
Kraus, Miiller, and others).”’ 
To summarize, fat is present in the kidney of the rabbit in 
the fresh condition which stains with sudan III after fixation with 
dichromate. After autolysis and fixation in an incubator, if 
osmic acid is present, there are some lipoids which will stain black. 
