Sidney Klein : 319 
may be mentioned in this connection the basal filaments of Solger, 94, 
which have been shown by the researches of Bensley, 96, Garnier, 00, 
Cade, 00, Zimmermann, 98, and others to be a structure common to 
many sero-zymogenic cells. Bensley, 96, 98, has also shown that the 
basal filaments correspond to the chromatin of the nucleus in their 
staining reactions and like the latter contain iron in the form of an 
organic compound and thus represent morphologically the substance 
presumably of nuclear origin which Macallum, 95, long ago discovered 
in gland cells of various sorts by means of staining reactions, and sub- 
sequently confirmed by means of the microchemical reaction for iron. 
As far as mucin is concerned no microchemical reaction has been, as 
yet, discovered, which is effective in recognizing this substance in 
isolated cells in sections. The work of P. Mayer, 97, has, however, 
provided us with a number of new staining solutions which, while they 
do not permit us to say whether a given cell does or does not secrete 
mucin, yet furnishes evidence which may be of much value when taken 
in connection with that from other sources. 
Up to the present no special attention has been directed to the ques- 
tion of the presence of Macallum’s prozymogen in the cells of Paneth, 
either in the form of basal filaments or as a diffused compound in the 
base of the cell, although several observers, notably Zipkin, 04, and 
Nicolas, have called attention to the deeper staining of the protoplasm 
of these cells as compared with neighboring cells. The results, more- 
over, of attempts to discover experimentally, differences in the aspect 
of these cells corresponding with phases of physiological activity have 
not been decisive. Accordingly, at the suggestion of Professor Bensley 
I undertook the reinvestigation of these structures in the hope that the 
application of new staining and microchemical methods would reveal 
new facts which would be of assistance in forming an opinion as to their 
nature and their relationship to other intestinal epithelial elements. 
At a very early stage in the investigation the discovery was made that 
in the opossum, Didelphys virginiana, the cells of Paneth occurred not 
only in the glands of Lieberkiihn but also mingled with other epithelial 
elements on the sides of the intestinal villi even at their very tips. This 
remarkable fact, which possesses no parallel in any other mammal, so 
far as is known, possesses so much significance in the interpretation of 
the Paneth cells that a somewhat extended description is called for. 
The small intestine of the opossum is characterized by extremely long 
villi and a very thin tunica mucosa. Corresponding to the latter the 
glands of Lieberkiihn are very short and contain a scarcely recognizable 
