78 
demonstrated that proteids and carbohy- 
drates are taken up by the biood and that 
they do not enter the lymphatic system. 
Natural fats are mixtures of the three 
chemical compounds—Olein, Palmatin and 
Stearin. Of these, the first is a liquid, the 
other two are solids. Consequently, the 
proportions in which these three ingredients 
are mixed conditions the melting point of 
the fat. Tallow and lard are high in 
stearin, while cod-liver oil is high in olein. 
Thus the melting point of fat enables us to 
form an idea as to what animal produced 
it. Butall fats, of whatever nature, reduce 
osmic acid, producing an intense black 
coloration, and this clear and distinctive 
test furnishes the reason why the absorp- 
tion of fat has been a favorite study with 
cell-physiologists. In passing a piece of 
intestine tissue through the various pro- 
cesses necessary for its microscopical study 
all nitrogenous bodies in solution in the 
cells are very probably dissolved out by the 
alcohols, but fat is only very slightly solu- 
ble in alcohol and not particularly so in 
cedar oil, and accordingly preparations that 
still contain a large part of their original 
fat contents may be studied. The error is 
more likely to be in the other direction ; 
osmic acid is reduced by all organic matter, 
and it is extremely probable that many cell 
aggregates, not fat at all, have, by virtue of 
their having actually reduced osmic acid, 
been mistaken for fat. 
Taking up now in detail what has been 
learned concerning the absorption of fat, we 
find that there are three conflicting theories. 
These are: 
1. Fat enters between the epithelial cells. 
2. Fat enters the epithelial cells. 
3. Fat enters both ways. 
Concerning the first of these views, that 
the only entrance path of fat is between the 
cells, it has had, in so far as I have been 
able to learn, but one advocate (Watney, 
1877), and the appearances are so strongly 
SCIENCE. 
[N.S. Vou. X. No. 238: 
against it that we are probably entirely safe 
in rejecting it in toto. 
With regard to the other views the mat- 
ter at issue is much more comprehensive 
than the mere entrance of fat. One of 
these, the second, holds that the sodium 
salt of a fatty acid (a soap) and glycerine 
enter the cell in solution. The reasons for 
believing this are, first, the general reason 
that the solids have never been known to 
enter the intestinal epithelium, and, second, 
the appearances in the fixed cell. The stri- 
ated border and a narrow band running 
across the cell just beneath the striated 
border are always free of fat.* It first ap- 
pears lower down in the cell and arises as 
exceedingly minute globules, which roll to- 
gether and fuse and eventually come to 
form masses, which may be so large that 
two or three fill the entire cell. That is, 
the soap and glycerine are synthesized, and 
fat appears in an exceedingly minute state 
of division. The increase in size of these 
particles is a merely mechanical phenome- 
non and has been observed in living cells. 
At the expiration of a certain period after 
the commencement of absorption a second 
process is inaugurated. This has been 
studied the most carefully in those forms 
which possess intestinal villi, and the fol- 
lowing is applicable to only such. A very 
fine canal system has been described by 
some, consisting of vessels that extend 
from the base of the cell into the lacteal, 
but more accurate observation has shown 
that such does not exist. The fat merely 
passes from the cell, the determining factor 
in its movement being protoplasmic activity, 
and becomes scattered throughout the 
stroma of the villus, lying in a peri-cellular 
fluid which occupies the spaces between the 
connective tissue cells and fibers. Heiden- 
hain (1888) has given a very clear expla- 
* This has been disputed. Some writers have de- 
scribed fat both in and just beneath the striated 
border. 
