DIGESTIVE PEOCESSES IN PLANAEIiE. 
211 
have shown that in the higher animals, especially in mammals, 
the absorption of fat by the epithelial cells of the intestine is 
brought about by the fat of the food being converted into 
fatty acids and glycerine by the action of lipolytic enzymes. 
Only in that form can the fat be taken up by the epithelial 
cells, which then again synthesise the fatty acids into fat, 
and the latter is seen in the cytoplasm of the cells in the form 
of globules, being passed on by them to the lymphatic cells 
and the lymphatic capillaries. 
The process appears to be very similar in the Planarim, 
and judging by the facts stated above, there is reason to 
believe that the goblet-cells of the Planarim function as 
organs secreting a lipolytic enzyme. Possibly they may 
elaborate other secretions as well, but their ability to secrete 
a fiit-digesting fluid can hardly be doubted. 
It has been pointed out that when the columnar cells are 
full of fat-globules stained by the osniic acid, no such fat is 
to be seen in the lutnen. It was therefore necessary to see 
whether there was any fat in the lumen in a form not acted 
on by osmic acid. It is well known that the staining with 
osmic acid is due to the presence of unsaturated compounds. 
In view of the work of Lorrain Smith (’07) it was thought 
desirable to test the action of Nile-blue sulphate, which 
stains not only the neutral fat, but differentiates the fatty 
acids. For this purpose some Planaria were fixed a quarter 
of an hour after feeding in a weak solution of foruiol and 
cut with a freezing microtome. By this means all fat solvents, 
such as xylol, etc., were avoided. The sections were then 
stained for fifteen minutes in a strong aqueous solution of 
the dye. In spite of the fact that the colour was slightly 
masked by the blue colour taken by all the tissue, charac- 
teristic globules of fat in the columnar cells were seen, red to 
reddish-yellow in colour. Care has to be taken not to 
confuse loose red blood-corpuscles which have been shifted 
from the lumen on to the cells with these globules. The 
colour is, however, entirely different, the fat-globules being 
definitely red under a high power lens, whereas the corpuscles 
