LIPOID CONTENT OF THE KIDNEY TUBULE 81 
Ten per cent potassium dichromate and osmic acid. Ten per 
cent potassium dichromate and 2 per cent osmic acid were used 
in the proportions of four to one and 35 cc. were acidified by 
three drops of glacial acetic acid. The tissue was subjected to a 
temperature of 51° for forty-eight hours. Material treated in 
this way showed the fat which reduces osmic acid more clearly 
and abundantly than tissue fixed in either Flemming’s or Benda’s 
fluid. In imbedding, both paraffin and parlodion were used, for, 
although more fat is preserved in parlodion sections, paraffin ones 
were found very useful in definitely locating the granules in the 
different regions of the tubule. 
The rays which were described as staining black in pieces of 
tissues fixed in Benda’s fluid stood out very clearly and intensely 
and the labyrinth was left unstained, except for some very fine 
granules (figs. 5 to 7). The same regions of the medulla were 
present as were described for material fixed in 10 per cent dichro- 
mate and stained with sudan IIJ. Here the outer zone appeared 
gray-black and the inner zone was left unstained. The large 
black globules were present in the medullary segment of the 
proximal convoluted tubule and were the same as those which 
stained intensely red and not at all or only at the periphery with 
sudan III. Other parts of the proximal convoluted tubule had 
very small granules at the base of the cells which did not stain 
an intense black. In the convoluted tubules of the kidney of a 
23-cm. kitten, there was the same linear arrangement of fine fat 
granules, though not so regularly placed, as may be found in the 
ascending limb of the medullary loop. These formations in the 
ascending limb will be described in the next paragraph. This 
linear arrangement of the lipoids in other portions of the urinary 
tubule besides the ascending limb may be due to the position 
of the lipoids in relation to mitochondria either passively or in 
consideration of a more intimate connection, or it may be an 
early stage of fat formation independent of mitochondria (fig. 
14). 
No lipoid was visible in the descending limb of the medullary 
loop which stained black with osmic acid. In the ascending 
limbs, those rods which, at times appeared granular and at other 
