deposited soon after delivery, and where it continues to be present during the whole period of the resorption or involution of this organ. In all these instances, the oleaginous matters remain distinct in form and situation from the other ingredients of the animal frame, and are only mechanically entangled among its fibres and cells, or imbedded separately in their interior. Fig. 15. A large part of the fat which is found in the body may be accounted for by that which is taken in with the food, since oily matter occurs in both animal and vegetable substances. Fat is, however, formed in the body, independently of what is introduced with the food. This important fact has been definitely ascertained by the experiments of MM. Dumas and Milne-Edwards on bees,' M. Persoz on geese, and finally by those of M. Boussingault on geese, ducks, and pigs. The observers first ascertained the quantity of fat existing in the whole body at the commencement of the experiment. The animals were then subjected to a definite nutritious regimen, in which the quantity of fatty matter was duly ascertained by analysis. The experiments lasted for a period varying, in different instances, from thirty-one days to eight months; after which the animals were killed and all their tissues examined. The result of these investigations showed that considerably more fat had been accumulated by the animal during the course of the experiment than could be accounted for by that which existed in the food; and placed it beyond a doubt that oleaginous substances may be, and actually are, formed in the interior of the animal body by the decomposition or metamorphosis of other proximate principles. MUSCULAR FIBRES OF HUMAN UTERUS three weeks after parturition. It is not known from what proximate principles the fat is produced, when it originates in this way in the interior of the body. Particular kinds of food certainly favor its production and accu Annales de Chim. et de Phys., 3d series, vol. xiv. p. 400. 2 Ibid., p. 408. 3 Chimie Agricole, Paris, 1854. mulation to a considerable degree. It is well known, for instance, that in sugar-growing countries, as in Louisiana and the West Indies, during the few weeks occupied in gathering the cane and extracting the sugar, all the negroes employed on the plantations, and even the horses and cattle, that are allowed to feed freely on the saccharine juices, grow remarkably fat; and that they again lose their superabundant flesh when the season is past. Even in these instances, however, it is not certain whether the saccharine substances are directly converted into fat, or whether they are first assimilated and only afterward supply the materials for its production. The abundant accumulation of fat in certain regions of the body, and its absence in others; and more particularly its constant occurrence in certain situations to which it could not be transported by the blood, as for example the interior of the cells of the costal cartilages, the substance of the muscular fibres of the uterus after parturition, &c., make it probable that under ordinary conditions the oily matter is formed by decomposition of the tissues upon the very spot where it subsequently makes its appearance. In the female during lactation a large part of the oily matter introduced with the food, or formed in the body, is discharged with the milk, and goes to the support of the infant. But in the female in the intervals of lactation, and in the male at all times, the oily matters almost entirely disappear by decomposition in the interior of the body; since the small quantity which is discharged with the sebaceous matter by the skin bears only an insignificant proportion to that which is introduced daily with the food. The most important characteristic, in a physiological point of view, of the proximate principles of the second class, relates to their origin and their final destination. Not only are they all of a purely organic origin, making their appearance first in the interior of vegetables; but the sugars and the oils are formed also, to a certain extent, in the bodies of animals; continuing to make their appearance when no similar substances, or only an insufficient quantity of them, have been taken with the food. Furthermore, when introduced with the food, or formed in the body and deposited in the tissues, these substances do not reappear in the secretions. They, therefore, for the most part disappear by decomposition in the interior of the body. They pass through a series of changes by which their essential characters are destroyed; and they are finally replaced in the circulation by other substances, which are discharged with the excreted fluids. CHAPTER IV. PROXIMATE PRINCIPLES OF THE THIRD CLASS. THE substances belonging to this class are very important, and form by far the greater part of the entire mass of the body. They are derived both from animal and vegetable sources. They have been known by the name of the "protein compounds" and the "albuminoid substances." The name organic substances was given to them by Robin and Verdeil, by whom their distinguishing properties were first accurately described. They have not only an organic origin, in common with the proximate principles of the second class, but their chemical constitution, their physical structure and characters, and the changes which they undergo, are all so different from those met with in any other class, that the term "organic substances" proper, appears particularly appropriate to them. Their first peculiarity is that they are not crystallizable. They always, when pure, assume an amorphous condition, which is sometimes solid (organic substance of the bones), sometimes fluid (albumen of the blood), and sometimes semi-solid in consistency, midway between the solid and fluid condition (organic substance of the muscular fibre). Their chemical constitution differs from that of bodies of the second class, first in the fact that they all contain the four chemical elements, oxygen, hydrogen, carbon, and nitrogen; while the starches, sugars, and oils are destitute of the last named ingredient. The organic matters have therefore been sometimes known by the name of the "nitrogenous substances," while the sugars, starch, and oils have been called "non-nitrogenous." Some of the organic matters, viz., albumen, fibrin, and casein, contain sulphur also, as an ingredient; and others, viz., the coloring matters, contain iron. The remainder consist of oxygen, hydrogen, carbon, and nitrogen alone. The most important peculiarity, however, of the organic substances, relating to their chemical composition, is that it is not definite. That is to say, they do not always contain precisely the same proportions of oxygen, hydrogen, carbon, and nitrogen; but the relative quantities of these elements vary within certain limits, in different individuals and at different times, without modifying, in any essential degree, the peculiar properties of the animal matters which they constitute. This fact is altogether a special one, and characteristic of organic substances. No substance having a definite chemical composition, like phosphate of lime, starch, or olein, can suffer the slightest change in its ultimate constitution without being, by that fact alone, totally altered in its essential properties. If phosphate of lime, for example, were to lose one or two equivalents of oxygen, an entire destruction of the salt would necessarily result, and it would cease to be phosphate of lime. For its properties as a salt depend entirely upon its ultimate chemical constitution; and if the latter be changed in any way, the former are necessarily lost. But the properties which distinguish the organic substances, and which make them important as ingredients of the body, do not depend immediately upon their ultimate chemical constitution, and are of a peculiar character; being such as are only manifested in the interior of the living organism. Albumen, therefore, though it may contain a few equivalents more or less of oxygen or nitrogen, does not on that account cease to be albumen, so long as it retains its fluidity and its aptitude for undergoing the processes of absorption. and transformation, which characterize it as an ingredient of the living body. It is for this reason that considerable discrepancy has existed at various times among chemists as to the real ultimate composition of these substances, different experimenters often obtaining different analytical results. This is not owing to any inaccuracy in the analyses, but to the fact that the organic substance itself really has a different ultimate constitution at different times. The most approved formulæ are those which have been established by Liebig for the following substances: Fibrin . Casein. = C299H228 N40092S2 = C298H228 N36090S2 Owing to the above mentioned variations, however, the same degree of importance does not attach to the quantitative ultimate analysis of an organic matter, as to that of other substances. This absence of a definite chemical constitution in the organic substances is undoubtedly connected with their incapacity for crystalli zation. It is also connected with another almost equally peculiar fact, viz., that although the organic substances unite with acids and with alkalies, they do not play the part of an acid toward the base, or of a base toward the acid; for the acid or alkaline reaction of the substance employed is not neutralized, but remains as strong after the combination as before. Furthermore, the union does not take place, so far as can be ascertained, in any definite proportions. The organic substances have, in fact, no combining equivalent; and their molecular reactions and the changes which they undergo in the body cannot therefore be expressed by the ordinary chemical phrases which are adapted to inorganic substances. Their true characters, as proximate principles, are accordingly to be sought for in other properties than those which depend upon their exact ultimate composition. One of these characters is that they are hygroscopic. As met with in different parts of the body, they present different degrees of consistency; some being nearly solid, others more or less fluid. But on being subjected to evaporation they all lose water, and are reduced to a perfectly solid form. If after this desiccation they are exposed to the contact of moisture, they again absorb water, swell, and regain their original mass and consistency. This phenomenon is quite different from that of capillary attraction, by which some inorganic substances become moistened when exposed to the contact of water; for in the latter case the water is simply entangled me chanically in the meshes and pores of the inorganic body, while that which is absorbed by the organic matter is actually united with its substance, and diffused equally throughout its entire mass. Every organic matter is naturally united in this way with a certain quantity of water, some more and some less. Thus the albumen of the blood is in union with so much water that it has the fluid form, while the organic substance of cartilage contains less and is of a firmer consistency. The quantity of water contained in each organic substance may be diminished by artificial desiccation, or by a deficient supply; but neither of them can be made to take up more than a certain amount. Thus if the albumen of the blood and the organic substance of cartilage be both reduced by evaporation to a similar degree of dryness and then placed in water, the albumen will absorb so much as again to become fluid, but the cartilaginous substance only so much as to regain its usual nearly solid consistency. Even where the organic substance, therefore, as in the case of albumen, becomes fluid under these circumstances, it is not exactly a solution |