1904-5.] ON THE ABSORPTION OF FAT IN THE INTESTINE. 253 
surface, these latter being especially numerous at the tip. As to the forces 
at work causing the fat to go towards the lacteal one can only offer con- 
jectures as to their character. Weymouth Reid* has shown that the 
epithelial cells of the intestine will absorb fluids when the osmotic pressure 
is negative and the hydraulic pressure less upon the lumen side so that in 
this case the vital activity of the cells must play the most important, if 
not the whole part. Certainly osmotic pressure cannot have anything 
to do with the transfer of fat through the lacteal since it depends for its 
results upon the number of dissolved molecules which in this instance is 
nil. The epithelial cells, by their contractions, can remove the fat from 
within them into channels which communicate with the lacteal; the 
contraction of the muscles about the chyle vessel which is supplied with a 
valve at its base empties the lacteal and the resulting dilation causes a 
relatively lower pressure so that the fat is forced to go in the direction 
of least resistance, probably by the stimulus received from the epithelial 
contraction. It is generally conceded that the proteid material normally 
goes by way of the blood vessels, but when fed along with excess of fat 
it frequently enters the chyle vessel with the fat. Fig. 11 shows that 
physical condijion cannot be overlooked in considering the causes of fat 
transferenge. 
Bruch} claimed to have demonstrated that the capillaries took up 
fat. He described certain vessels as half filled with fat, the other half 
showing the normal blood reaction. Heidenhain has g¢riticized Bruch’s 
work and concludes that his technique was very faulty in that the whole 
section showed up more or less black owing to the fixing agent not having 
been washed out before placing in alcohol. I have never been able at any 
time to satisfy myself that any fat ever entered the blood capillaries, 
probably because, as Heidenhain suggests, the fat in the parenchyma is 
not in a sufficiently divided condition to enter them. Fat, undoubtedly, 
in other parts of the body, leaves the capillaries for the tissues, but it 
must be as very minute particles indeed, and if it can leave the capillary 
its passage in the opposite direction should not be an impossibility, but 
from experiments upon the percentages of fat in the portal vessels as 
compared with such vessels as the carotids and femorals the probability 
of fat entering the capillaries of the villi is negative. 
As to the part supposed by some to be played by leucocytes as agents 
in transferring fat to the lacteal it may be stated that in the guinea pig, 
evidence of such an activity, except as a rare feature, cannot be found, 
and in fact the presence of leucocytes within the lacteal is a rare occur- 
* Phil. Trans. Roy. Soc., Vol. 192B, 1900, p. 211. 
+ Zeit. fiir wiss. Zool., Vol. 4, 1853, p. 288. 
