As no other agents present themselves for fulfilling the sweet object in view, we have been in the habit of preparing emulsions without attempting to make them sweet, and, we believe, without detracting from their palatability, while enhancing their appearance.
Now, then, let us consider what agent will favour the homogeneity of the emulsion, that is, prevent separation or precipitation, bearing in mind that the preparation must not be changed physically or chemically.
Gelatine has been used with some satisfaction, as it retards the separation for a considerable length of time; in fact, it answers the purpose so well that for the extemporaneous preparing of emulsions it leaves nothing to be desired. But in common with other agents used for this purpose, it gradually loses its power of preserving the homogeneity of an emulsion, and eventually the separation and decomposition, so-called, alluded to above, take place.
The proportion of gelatine employed is about 40 gr. to 1 pint of the emulsion; it should be dissolved in the water and added at any time of the operation. By increasing this amount so that a jelly is formed of the emulsion, a perfectly permanent and stable preparation is obtained. But this result is obtained because the physical character of the emulsion has been changed - fluidity abandoned for consistence. Unhappily we cannot take advantage of this condition, and therefore "consistence is not a jewel" pharmaceutically.
Chemical agents such as change the character of an emulsion by saponifying the oil, have been largely advocated, and to the employment of this class of substances is principally due the elegance and permanence of ready-made emulsions. That this is attained at the sacrifice of the medicinal value of the preparation, we have no doubt, but medical authorities have also demonstrated it to be a questionable procedure to chemically change the constitution of a fat intended for internal administration by what should be a simple pharmaceutical process - emulsification, and now condemn the use of alkalies with balsams and resins. Copaiba is no more exhibited with solution of potash, and alkalies are generally conceded as operating to break up the sensitive electronegative principles of resins, upon which their medicinal value chiefly depends. Animal fat, and especially cod liver oil when rendered alkaline, undoubtedly suffers decomposition in those very constituents to which its superior digestibility is due, and thus what has been gained on one hand is more than lost on the other.
The saponification which has been produced by the use of the alkali renders the preparation very prone to rancidity if exposed to the air, and even when freshly made, it possesses inferior palatability, but then this has been of secondary importance to homogeneity or elegant appearance.
But our materia medica is vast in extent, and we have yet another quarter to draw upon, namely, the animal kingdom. It was a rational thought which prompted the employment of egg-yelk as an emulsifying agent, and how well it answers the purpose, we are all familiar with. Egg-yolk unfortunately does not belong to the general armament of a pharmacy, and a convenient and stable form thereof was therefore suggested in the preparation glyconin, a mixture of egg-yolk and glycerine in about equal proportions. Although the proportion of glyconin required for emulsifying oil is small, about 1 to 4, and therefore the quantity of glycerine in the finished emulsion not very great, we prefer to use the fresh yolk alone when this can be obtained.
Egg-yolk sometimes possesses advantages as an emulsifying agent over gum acacia when this latter is inadmissible on account of the precipitation that would take place when alcoholic liquids are desired in the combination. The following prescription is typical of the class of preparations in which it will prove a valuable agent:
Take of Copaiba ........ 2 oz.
Oil Almonds, Exp..... 4 „
Oils Gaulther. and Sassafras, each ...... 20 m.
Egg-yolk (or Glyconin, 3) 1 1/2 oz.
Water.......... 4 „
Turpentine pitch .. .. 1 „
Spirit Nitrous Ether.. .. 4 „
Make an emulsion as described under gum acacia. Dissolve the turpentine in the spirit of nitrous ether, and add it to the emulsion.
But it has been reserved to physiological chemistry to discover upon the whole the most rational and valuable of all emulsifying agents. Not valuable in the sense that the preparations are either permanent or homogeneous, but valuable because the emulsification is the most natural, and attained with the least change only in so far as its superior assimilative qualities are concerned. That preference should be given to such agent in preparing an artificial emulsion as fulfils this mission in the animal or human body we cannot deny, providing it is enable of practical application; that is, if this agent can be'obtained in as natural a form as necessary to serve this same purpose artificially. Pancreatine, as is well known, is that peculiar principle which is secreted by the pancreatic gland in animals, performing the function of emulsifying fats so as to prepare them for assimilation in the economy. Modern therapeutists, reasoning that maladies such as indigestion or malassimilation of food, especially of a fatty character, would be benefited by this agent sup plied artificially, have had their expec-tations realised in no small degree, and pancreatine has therefore met with increasing favour.
Although believed to he a complex substance, and to possess digestive powers identical with those of pepsine and ptyaline, yet it seems un-oubtedly to exercise its greatest power on tats, decomposing them in glycerine and fatty acids, thus fitting them for ready absorption.
Pancreatine has been largely prescribed in substance, bat of this we have nothing to say, as our observations are in regard to its pharmaceutical use. The pancreatine obtained from the fresh pancreas of the calf, vulgarly termed sweetbreads, has been most successful in our hands, and we feel confident that as an emulsifying agent it will be found superior to that obtained from the hog or sheep.