in the epithelial cells were made from absorbed fatty acid. Further, the observation has been made that the fat particles in the epithelial cells are small at the beginning of intestinal digestion, but that they grow larger when the digestion has been in progress some time, as though the droplets were made at the point where they are seen. Again it has been shown that the fat ferment in the small intestine is abundantly able to convert the fat of an ordinary meal completely into fatty acid in the time usually required for a meal's digestion.
However, it seemed difficult to understand how a drop of fat in contact with an epithelial cell was first converted into fatty acid, then absorbed by the cell and, before leaving the confines of the absorbing cell, reconverted into a droplet of fat. But a similar transformation is believed to occur in the case of proteid absorption. Proteids in digestion are converted into peptone and thus absorbed, but no peptone is found in the body, not even in the intestinal blood vessels, hence the peptones must be at once reconverted into other proteids in the act of absorption.
The work of Kastle and Loewenhart makes it clear, in the case of fat, how the reverse processes are brought about. Before referring to their work let us remark that it is well known that the action of ferments is never complete unless the product of the fermentation is removed. To illustrate—if grape juice is fermenting to become wine, the conversion of sugar to alcohol at first may be quite rapid, but by the time a wine of ten per cent, alcohol is formed the alcohol present inhibits the further action of the ferment. If the alcohol could be removed from the wine, the action of the ferment would continue so long as there was sugar present to ferment.
Further, it has been shown that the action of a ferment may be reversible, i. e., that the same ferment which will convert a solution of carbohydrate A into carbohydrate B will also convert a solution of carbohydrate B into a carbohydrate A. But, as just mentioned, the action of no ferment is complete, hence whether we start with a solution of A or of B, the ferment action brings about a solution of A and B in such proportion that ferment action ceases, i. e., the condition has become one of chemical equilibrium. Kastle and Loewenhart worked with the ferment lipase, whose known action was the conversion of neutral fats into fatty acid and glycerine. They added the ferment to a solution of fatty acid and were able to demonstrate the formation therefrom of the neutral fat.[1] The importance of this observation is very great. First, it adds another to the list of animal synthetic processes. Second, it offers an easily comprehended explanation of the absorption of fat. For in case the small intestine contains neutral fat immediately after a meal, the ferment will soon begin to convert
- ↑ They employed butyric acid and synthetized ethyl butyrate.
