The inferences drawn by M. Edwards from the whole of the experiments are the following: ‘1. That gelatin alone is insufficient for alimentation. 2. That, although insufficient, it is not unwholesome. 3. That gelatin contributes to alimentation, and is sufficient to sustain it when it is mixed with a due proportion of other products which would themselves prove insufficient if given alone. 4. That gelatin extracted from bones, being identical with that extracted from other parts—and bones being richer in gelatin than other tissues, and able to afford two-thirds of their weight of it—there is an incontestable advantage in making them serve for nutrition in the form of soup, jellies, paste, &c., always, however, taking care to provide a proper admixture of the other principles in which the gelatin-soup is defective. 5. That to render gelatin-soup equal in nutritive and digestible qualities to that prepared from meat alone, it is sufficient to mix one-fourth of meat-soup with three-fourths of gelatin-soup; and that, in fact, no difference is perceptible between soup thus prepared and that made solely from meat. 6. That in preparing soup in this way, the great advantage remains, that while the soup itself is equally nourishing with meat-soup, three-fourths of the meat which would be requisite for the latter by the common process of making soup are saved and made useful in another way—as by roasting, &c. 7. That jellies ought always to be associated with some other principles to render them both nutritive and digestible.’[8]
The reader may make a very simple experiment on himself by preparing first a pure gelatin-soup from isinglass, or the prepared gelatin commonly sold, and trying to make a meal of this with bread alone. Its insipidity will be evident with the first spoonful. If he perseveres, it will become not merely insipid, but positively repulsive; and, should he struggle through one meal and then another, without any other food between, he will find it, in the course of time (varying with constitution and previous alimentation), positively nauseous.
Let him now add to it some of Liebig’s ‘Extract of Meat,’ and he will at once perceive the difference. Here the natural appetite foreshadows the result of continuing the experiment, and points the way to correcting the errors of the Academicians and Baron Liebig. The jellies that we take at evening parties, or the jujubes used as sweetmeats, are flavoured with something positive. I have tasted ‘Blue-Ribbon’ jellies that were wretchedly insipid. This was not merely owing to the absence of alcohol, of which very little can remain in such preparations, but rather to the absence of the flavouring ingredients of the wine.
I venture to suggest the further, deliberate, and scientific extension of this principle, by adding to bone-soup, or other form of insipid gelatin, the potash, salts, phosphates, &c., which are found in the juices of meat and vegetables. They may either be prepared in the manufacturing laboratory, like Parrish’s ‘Chemical Food,’ or ‘Syrup of phosphates,’ or extracted from fruits, as commercial limejuice is extracted. I recommend those who are interested to manufacture and offer for sale a good preparation of limejuice gelatin.
It would seem that gelatin alone, although containing the elements required for nutrition, requires something more to render it digestible. We shall probably be not far from the truth if we picture it to the mind as something too smooth, too neutral, too inert, to set the digestive organs at work, and that it therefore requires the addition of a decidedly sapid something that shall make these organs act. I believe that the proper function of the palate is to determine our selection of such materials; that its activity is in direct sympathy with that of all the digestive organs; and that if we carefully avoid the vitiation of our natural appetites, we have in our mouths, and the nervous apparatus connected therewith, a laboratory that is capable of supplying us with information concerning some of the chemical relations of food which is beyond the grasp of the analytical machinery of the ablest of our scientific chemists.
What is the chemistry of the cookery of gelatin? What are the chemical changes effected by cookery upon gelatin? Or, otherwise stated, what is the chemical difference or differences between cooked and raw gelatin? I find no satisfactory answer to these questions in any of our text-books, and therefore will do what I can towards supplying my own solution of the problem.
In the first place, it should be understood that raw gelatin, or animal membrane as it exists in its organised condition, is not soluble in cold water, and not immediately in hot water. Genuine isinglass is the membrane of the swim-bladder of the sturgeon (that of other fishes is said to be sometimes substituted). In its unprepared form it is not easily dissolved, but if soaked in water, especially in warm water, for some time, it swells. The same with other forms of membrane. This swelling I regard as the first stage of the cookery. On examination, I find that it is not only increased in bulk but also in weight, and that the increase of weight is due to some water that it has taken into itself. Here, then, we have crude gelatin plus water, or hydrated gelatin. Proceeding further, by boiling this until it all dissolves, and then allowing it to harden by very slow evaporation, I find that it still contains some of its acquired water, and that I cannot drive away this newly-acquired water without destroying some of its characteristic properties—its solubility and gluey character. Before returning to its original weight as crude isinglass, it becomes somewhat carbonised.
Hence, I infer that the cookery of gelatin consists in converting the original membrane more or less completely into a hydrate of its former self. According to this, the ‘prepared gelatin’ sold in the shops is hydrated gelatin, completely hydrated, seeing that it is completely and readily soluble.
The membranes of our ordinary cooked meat are, if I am right, partially hydrated, in varying degrees, and thereby prepared for solution in the course of digestion. The varying degrees are illustrated by the differences in a knuckle of veal or a calf’s head, according to the length of time during which it has been stewed, i.e. subjected to the hydrating process.
The second stage of the cookery of gelatin is the solution of this hydrate, as in soups, &c.