When food is taken into the mouth, its presence stimulates through the nervous arrangement; the salivary glands to produce a copious flow of saliva, which during mastication is (or ought to be) thoroughly mixed with the food. Aside from a slight conversion of starch into sugar, the act of mastication is purely mechanical the food is broken up, lubricated and gathered into proper form to be swallowed. The temperature in the mouth is 100 degrees Fahrenheit, and of course, any free fat whose melting point is at or below this temperature, will liquefy. The chemical reaction of saliva is alkaline.

When the food reaches the stomach, its presence, as in the mouth, acts as a stimulus and causes an increased secretion, which had already begun when the food was taken into the mouth, of the acid fluid called gastric juice.

The muscular construction of the stomach keeps the food in constant motion so that it is thoroughly mixed with the gastric juice. When the bolus of food mixed with saliva comes in contact with the acid gastric juice the conversion of starch into sugar ceases; the proteids are broken up and dissolved; the proteid cell-walls of the adipose tissue are dissolved, which sets the fat-drops free; and the free fats which liquefy at or below 100 degrees, or perhaps 101 degrees Fahrenheit, which is the highest temperature in the stomach, are melted and to some extent, emulsified and split up into fatty-acid and glyceryl. The acidity of the gastric juice is essential to its activity.

As the food is dissolved or digested (it is now called chyme), it is mostly carried into the intestines by the muscular action of the stomach where it is met by three other digestive fluids; the bile, pancreatic juice and intestinal juice, which are all alkaline in reaction. When the chyme leaves the stomach it is, under normal conditions, acid; but as it is mixed with these alkaline fluids its acidity is neutralized and its reaction becomes alkaline.

In the intestine the conversion of starch into sugar takes place with great rapidity and the proteids or peptones, as they are called after being acted upon by the pepsine of the gastric juice, are still further broken up. The pancreatic juice, so far as is known, is the chief agent in bringing about these changes. The bile does nothing more than to aid in neutralizing the acidity and thus prepare them for the action of the pancreatic juice. But with fat it becomes an important factor. Its salts unite with any free fatty acid and form soaps. It also dissolves soaps which, as we shall see hereafter, materially aid the pancreatic fluid in its action upon fats. Bile also has some emulsifying power on fats. A soap is a fat acid united with a base, as soda, potash, etc.

The pancreatic juice has a powerful emulsifying effect upon fats; that is, divides them into very minute particles. It also has the power, to some extent, of breaking them up into their fatty acid and glycerine; and if an alkali is present the fatty acid unites with it to form soap.

As we have already stated, bile has a slight emulsionizing and solvent effect upon fat, but the fact which is known to be the most important in its relation to the digestion of fat is, that it unites with the free fatty acids which are present in the chyme and forms soaps. It also dissolves soaps that may have been formed before reaching it;

and the presence of soluble soaps are known to aid the emulsion of fats.

Foster says in reference to this: "Thus a rancid fat, i. e., a fat containing a certain amout of free fatty acid, forms an emulsion with an alkaline fluid more readily than does a neutral fat. A drop of rancid oil let fall on the surface of an alkaline fluid, such as a solution of sodium carbonate of suitable strength, rapidly forms a broad ring of emulsion and that even without the least agitation. As saponification takes place at the junction of the oil and alkaline fluid, currents are set up, by which globules of oil are detached from the main drop and driven out in a centrifugal direction. The intensity of the currents and the consequent amount of emulsion depend on the concentration of the alkaline medium and on the solubility of the soaps which are formed; hence some fats, such as cod-liver oil, are much more easily emulsionized in this way than others. Now, the bile and pancreatic juice supply just such conditions as the above for emulsionizing fats; they both together afford an alkaline medium. The pancreatic juice gives rise to an adequate amount of free fatty acid, and the bile in addition brings into solution the soaps as they are formed. So that we may speak of the emulsion of fats in the small intestine as being carried on by the bile and pancreatic juice acting in conjunction, and as a matter of fact the bile and pancreatic juice do largely emulsify the contents of the small intestine, so that the grayish turbid chyme is changed into a creamy looking fluid, which has been sometimes called chyle.'

Now, we believe that butter fat is especially fitted to supply these conditions. Butter, as is well known, readily becomes rancid and no doubt butter contains some free acid very shortly after being made, but we will consider a perfectly fresh specimen. According to Lang, the first step in the decomposition of butter is a conversion of lactic acid into butyric. The second is the breaking up of butyrine into butyric acid and glycerine, the butyrine furnishing by far the most free acid, about seven per cent.t Thus we see that the first fat in the mixture of butter to break up outside of the body is butyrine, and doubtless this is the case inside.

J. Bell, asserts that when a solution of alcohol and an alkali is used in insufficient quantity to saponify all the butter fat treated, the alkaline base unites with the soluble fatty acids and what is left undecomposed are the fats containing the insoluble fatty acids. He also illustrates this by relating an actual experiment. This strongly corroborates the supposition that it is the butyrine that is first broken up in the stomach and intestines.

We have seen in the process of stomach digestion that some fat was emulsionized and broken up into its acid and glycerine constituents. So we have butyric acid set free in the stomach to unite with a base from some of the weaker salts, as the carbonates, for instance, to form a very soluble soap which is dissolved by the bile as soon as it comes in contact with it, and thus furnishing, even a fresh butter, the most favorable conditions for starting the action of the pancreatic juice.

upon fats. Indeed Roberts* claims that a small admixture of a free fatty acid in the chyme together with the agitation produced by the movements of the intestines is sufficient to emulsify fats without the aid of pancreatic juice.

Routh also declares the same. None of the other animal fats contain butyrine.

The large proportion of butyrine in butter and its non-occurrence in any of the other animal fats together with the volatility of its acid, has long impressed us with the belief that it had some important office to perform in the digestive process. Under this belief we began a series of experiments upon the artificial digestion of different fats. Our digestive fluid was composed of five grains of Fairchild Bros. and Foster's "Extractum pancreatis," five grains of bicarbonate of soda dissolved in ten c. c. of distilled water. After the solution was complete we added half a dram of melted fat.

The whole was well agitated in a test tube and placed in an oven at a temperature of from 100 to 101 degrees Fahrenheit. The fats experimented on were cod-liver oil, butter, oleomargarine butter, the commercial oleomargarine oil, lard oil, benne oil, cotton-seed oil, lard, and mutton and beef suet. The cod-liver oil was bought from a reliable drug store.

Both fresh and stale butter was used, and was such as we had made ourselves seeing the milk from which it was made drawn from the cow, or such as we had analyzed ourselves and found to be pure, cow's butter. Fresh and stale "oleo" was used and was also either made by ourselves under the "Nathan" patent, which "oleo" contained some free acid, or was that which we had analyzed. The oils were all obtained

from "oleo" makers or dealers in New York city. Both the pure washed dry fats of the butters and "oleos" and the natural products were compared as will be described directly. The contents of the test tubes were examined under a microscope at intervals of one, two, three, four, six, twelve, sixteen and twenty hours.

The cod-liver oil nearly always showed the finest emulsion.

Next, and the difference was often just perceptible came genuine butter. See Plate I. "Oleo" and lard oil came next, there being frequently no appreciable difference between them, but between the butter and the "oleo" there was a marked difference at the end of each period.

Fig. 4, Plate I, and Fig. 1, Plate II, shows the difference between "oleo" and genuine butter after being acted upon by the digestive fluid for one hour. It will be noticed that there is no emulsion at all of the "oleo" while the butter is well advanced.

Fig. 5, Plate I, and Fig. 2, Plate II, shows the same at the end of four hours. It is seen that the "oleo" is not nearly as much emulsified as the butter was at the end of one hour.

Fig. 6, Plate I, and Fig. 3, Plate II, presents the same at the end of twelve hours, which shows that the "oleo" is but a trifle, if at all, further emulsionized than the butter was at the end of the four hours.

*Indigest. and Biliousness, Fothergill, page 53. + Routh, On Infant Feeding, page 131, 3d ed.