452 CHEMISTRY OF THE DIGESTIVE PROCESSES. 
only melts at 62° C, such a thing could not occur in the frog's intestine. 
Moreover, a microscopic examination of the intestinal contents at the 
end of an experiment showed only amorphous masses of fatty acid and no 
emulsified globules. Will concludes that the fatty acid must be absorbed 
as a soap and not as an emulsion. 
That the mucous membrane of the small intestine is capable of 
taking part in such a synthetical process, is shown by experiments of 
Ewald, 1 who dried the mucous membrane of a dog's intestine, which had 
been killed in a condition of hunger, at a low temperature after the 
method introduced by Brown and Heron, 2 and showed that this was 
capable of inducing the formation of neutral fat, from a mixture in 
proper proportions of soap and glycerin. 
This experiment shows that, provided glycerin and soap are formed 
in the intestine, there is an agency provided for synthesising them 
back into neutral fats. Let us next consider what the probabilities are 
that such a complete decomposition, into fatty acids and glycerin 
followed by solution of the fatty acids as alkaline soaps, takes place in 
the intestine. 
The idea that only a small fraction of the fats is decomposed in 
the alimentary canal into fatty acids and glycerin, has arisen from 
repetition of the emulsion theory only, and not from any experimental 
observation of lack of intensity of action of the fat-splitting ferment. 
Hoppe-Seyler 3 found that most of the fatty matter in both small and 
large intestine was composed of stearic and palmitic acids accompanied 
by very little neutral fat, and concludes that the decomposition into the 
fatty acids and glycerin is much greater than is usually supposed. 
Eachford 4 states that pancreatic juice must act very rapidly on fats, 
under the favourable conditions found in the duodenum, and is capable, 
unless checked or retarded in some manner, of splitting all the fats of 
the food into fatty acids and glycerin in the time required for intestinal 
digestion. 
It may be concluded, then, that there is sufficient fat-splitting power 
provided in the intestine for the complete conversion of the fats into 
fatty acids; and it has been already pointed out that, on feeding with 
fatty acids or with soaps, these are absorbed, and converted into fats in 
the process. It only remains to consider, in connection with the soap 
theory, whether, in the natural process of fat digestion and absorption, 
it is probable that the fatty acids so set free combine with alkalies to 
form soaps, or whether they are absorbed in some other soluble form. 
It has been objected to the theory of absorption in the form of 
soaps, that the reaction of the small intestine in the dog during fat 
absorption is not alkaline, but acid ; that soaps cannot persist in 
presence of an acid reaction, and hence that fats cannot be absorbed 
as soaps. 
Cash 5 investigated the reaction of the intestine in three experiments on 
dogs, in which the animals were fed on a mixture of starch and fat, and in 
three similar experiments in which the animals were fed on fat alone. He 
1 Arch. f. Anat. u. Physiol., Leipzig, 1883, Supp. Bd., "Festschrift f. dn Bois-Rey- 
mond," S. 302, Vorlaufige Mittheilung. 
- Proc. Roy. Soc. London, 1880, p. 393. 
3 Virchoio's Archiv, ]863, Bd. xxvi. S. 534, Anmerkung. 
4 Jowrn. Physiol., Cambridge and London, 1891, vol. xii. p. 92. 
5 Arch./. Anat. u. Physiol., Leipzig, 1880, S. 323. 
