30 E. V. COWDRY 
our hypothesis is correct, this reversal would mean the temporary 
passage of material from the lumen in the direction of the per- 
ipheral blood vessels. Absorption from the lumen, which nor- 
mally takes place to some extent, is probably accelerated as a 
result of the operation. We would not expect to be able to 
induce so simply experimental reversal in the position of the 
reticular material in the acinus cells of the pancreas or in the 
salivary glands, because absorption, with the accompanying 
tendency to the production of a current in an unusual direction, 
is in them at a minimum. 
Basile (714, p. 3) discovered that unilateral nephrectomy pro- 
duces definite changes, possibly compensatory in nature, in the 
reticular material of the remaining kidney. From its normal 
position between the nucleus and the lumen it migrates, in both 
the tubuli contorti and recti, to a new position between the nu- 
cleus and the base of the cell. This would, in my judgment, indi- 
cate the predominance of absorption over excretion and would 
seem to pave the way for a study of the physiology of the kidney 
from a new angle. 
But we are laboring more or less blindly because so little is 
known regarding the true nature of the reticular material. The 
chief difficulty is that we have thus far been unable to study it 
directly in living cells. It is a simple matter to give a long list 
of chemicals which destroy it during fixation, and to enumerate 
stains, like. resorecin-fuchsin, which have been known in rare 
instances to color it, without mentioning any positive reaction of 
value. By virtue of its affinity for silver (methods of Golgi and 
Cajal) and of the fact that it blackens after prolonged treatment 
with osmic acid (method of Kopsch), it may be studied closely 
in fixed tissues. Though both of these methods are more or less 
unsatisfactory, the results which they yield are always mutually 
confirmatory; so that one is justified in concluding that by their 
characteristic morphology and location, the blackened networks 
reveal the existence of some unknown and hitherto unrecognized 
material in the living cell. This conclusion is supported by the 
further observation that fixation in several fluids, such as Zenker, 
under certain conditions, and a mixture of formalin, potassium 
