The principal constituents of fat, therefore, are carbon and hydrogen. Again, chemistry teaches that all food not consisting of flesh, such as vegetables, farinacea, sugars, &c., resemble fat, being chiefly composed of carbon and hydrogen; and, still more, that fat exists, already formed, in some vegetable substances, as oil of olives, oil of nuts, and oleaginous seeds. If, therefore, we introduce into the system substances rich in carbon and hydrogen, we must make fat as inevitably as the bee makes honey from its elements contained in the flowers.

On the other hand, we learn also from chemistry, that one of the principal constituents of meat is nitrogen, an element which does not enter into the composition of fat. Food consisting chiefly of meat must be less productive of fat than food mainly composed of carbon and hydrogen, such as vegetables, &c.

Distinguished chemists have endeavoured to shew in what manner the development of fat takes place in the animal economy. A paper was read by me before the Academy of Sciences, at Paris, on the 15th December, 1851, from which the following extract is made:

"Three different opinions are entertained by distinguished chemists, who have given attention to this subject. The first, that of Dumas, maintains that the fatty matter of the body is derived solely from substances analogous to fat in composition, which pre-exist in the food. The second opinion, that of Liebig, is to the effect that the formation of fat is due to a modification of those ternary compounds which constitute so large a proportion of the food of animals. The third opinion suggests that fat may arise in consequence of some special fermentation taking place in the stomach.

"Numerous experiments have been made, in order to determine which of these opinions is correct; but it may be safely said that no satisfactory conclusion has been arrived at.

"In the first place, the experiments have never been conducted under circumstances favourable to the formation of a correct opinion. It is obviously of the first importance, when conducting experiments of this nature, that the food should be supplied so as not to interfere with the tone of the general health, considered morally as well as physically. We can conceive that the deprivation of liberty, in the case of an animal usually in the enjoyment of freedom, may render the experiment of dubious import. Although man is omnivorous, it is impossible that any one can submit, for a great length of time, to live upon one kind of food only, without suffering a sense of loathing.

"What inference can be drawn from those experiments, made for the purpose of ascertaining whether sugar is capable of producing fat, when they were made upon pigeons and doves, which were fed solely upon this substance; at one time being deprived altogether of water, and at another time allowing them as much as they chose to drink?

"Chemists wished to know if butter could engender fat, and doves have been gorged with it, being deprived of all other food during the few days that the experiment lasted; at the end of which time they died, of course excessively lean; and the experimentalists thence concluded that butter does not produce fat. What an extraordinary idea, to feed a granivorous animal upon butter solely, in order to test the question referred to! This experiment forms the subject of a paper written by me, and inserted in the proceedings of the Academy of Sciences, for the year 1844.

"Other experiments upon animals, conducted likewise by men of science, are less open to criticism than the one just referred to; yet it must be confessed that no safe inference could be drawn from them. I am about to submit a few established facts, which may throw some light upon the question as to the cause of the development of fat.

"For several years past I have given much consideration to the reduction of corpulency in cases where it interfered with the comforts of life, and I can reckon by thousands those who have followed my instructions. I have established it as a fact, without a single exception, that it is always possible to diminish obesity, by living chiefly upon meat, and partaking only of a small quantity of other kinds of food. Make use of whatever medicine you please, it is impossible to obtain the same result in the case of a person partaking indiscriminately of everything which may be placed upon the table. There is yet another condition, without which success is impossible; that is, to absorb but little fluid, whether in the shape of soup or drink, or by means of the bath. A moist atmosphere is favourable to the development of fat: we increase in weight in wet weather.

"I have thousands of cases on record, in support of my statement. Persons from all parts of the world, who have followed my teachings, have experienced a decrease of their corpulence."

The paper upon this subject ended by saying, that according to my opinion, fat might be assimilated by either of the three several methods set forth in the beginning of the essay, one not forbidding the action of the others. I begged to be acknowledged by the Academy as the first who had established the fact that, in order to reduce corpulence without interfering with the general health, it is necessary to live chiefly upon meat, avoiding an excess of vegetable and aqueous food, or of any of which the basis is carbon or hydrogen.