E . PULSION THEORIES OE EA T ABSORPTION. 449 
that existing immediately after such a discharge from the stomach, while the 
emulsion condition is a Liter stage. 
In whatever form fats may be absorbed from the intestine, it is certain 
that previous emulsification must, greatly assist the digestive fluids, by 
exposing an infinitely greater surface to their action. It is also certain that 
in a great many cases, if not in all, previous emulsification does take 
place. 
Emulsion theories of fat absorption. — It was for a long time a 
popular theory that only a small fraction of fat is split up in the intes- 
tine into fatty acid and glycerin; and that by means of the small 
amount of acid so formed, aided by that present in the fat as it leaves 
the stomach, the remainder of the fat is converted into a fine emul- 
sion which passes as such into the villi, and reaches the central lacteal. 1 
Such a statement may be found in most text-books, but the progress of 
recent work has had a tendency to cast grave doubts on its truth, and 
to show that, at least as a general statement, it is erroneous. The theory 
does not rest on any direct observation of the amount of fat which 
leaves the intestine as emulsified fat, compared with that which leaves 
it in other forms, such as soap, glycerin, and emulsified fatty acids, 
— such a direct observation, in the present state of our knowledge, is 
impossible, — but on indirect evidence, which is briefly as follows: — 
1. The presence of a very small percentage of fatty acid is all that 
is necessary in presence of an alkaline solution to perfectly emulsify 
neutral fat. 
2. This small amount of free fatty acid can readily be furnished by 
the action of the pancreatic enzyme even on neutral fats, and to aid this 
action all fats contain already some fatty acid mixed with them. The 
alkaline juices poured into the intestine are capable of supplying the 
alkali necessary for emulsification. 
3. When an animal is killed during active fat digestion, the lacteals 
invariably contain a white milky emulsion, consisting mainly of neutral 
fats with a small percentage of alkaline soaps. 
Therefore the most natural conclusion is that a fine emulsion is 
formed in the intestine which passes in some manner into the lacteal. 
The greater part of the fat is only physically, not chemically, 
altered in digestion, and passes through the whole process as a neutral 
fat. 
The weak point in the emulsion theory of absorption always was, 
how the fat globules got into the interior of the villus and made their 
way to the lacteal. Although the fat granules in an emulsion are of 
microscopic dimensions, they are still large compared to the dissolved 
molecules of serum or egg albumin which are unable to pass into or out 
of the intestine through the epithelial cells. If fat grannies pass into 
the epithelial cells at all, it must therefore be by means of a 
special kind of absorption in bulk by these cells, aud not by a process 
even of selective diffusion from solution. Such an absorption by bulk is 
easily carried out by a cell of which the protoplasm is capable of free 
contraction, such as the aniceba, or leucocyte, but it is difficult to conceive 
how it can take place with a fixed cell, such as those which line the 
intestine. Impressed, perhaps, with the necessity of some such proto- 
plasmic movement, some observers have looked earnestly for proto- 
1 This theorv was first stated by Briicke, Sitzimgsb. d. k. Akad. d. Wissensch., Wien, 
1870, Bd. lxi. Abth. 2, S. 362. 
VOL. I. — 29 
