These results, when reduced and tabulated, give― Tabular view. mative. The juice of possibly flesh may contain no It is hardly necessary to state, that these num- These numbers only bers only express approximatively the proportions of approxipotash to soda in the flesh, because it is impossible to obtain the juice of the flesh of the ox, horse, and fowl, free from blood and lymph, fluids which contain much soda. Had it been possible to obtain the juice of flesh unmixed with blood and lymph, the proportion of potash to soda would have come out much higher; so much so, indeed, that the conclusion, soda. that salts of soda form no part of that fluid, is not destitute of probability; and if, as is supposed, the lymphatic vessels possess the power of taking up the salts of soda which pass from the capillaries into the substance of the muscles, and returning these salts to the larger blood-vessels, the fact just mentioned admits of a very simple explanation. The permeability of the vessels of the va rious fluids must be From the great difference of chemical nature and qualities in the fluids circulating in the different parts of the organism, it follows, that there must be a very remarkable difference in the permeability different. of the parietes of the vessels for these fluids. Were this permeability in all cases the same, there must have been found as much of the salts of soda and potash in the juice of flesh as in the blood; but the Potash preponderates in milk. Accumulation of free acids in some morbid states, causing the disappear ance of the bones. Importance 108 IMPORTANCE OF CHLORIDE OF SODIUM blood of the ox and the fowl contains nearly a third of its whole saline contents of chloride of sodium, while hardly a trace of this compound occurs in the juice of flesh. The vessels which secrete milk must stand in a similar relation to the blood-vessels; for in the milk of the cow, the salts of potash preponderate very greatly over those of soda, and are present also in much larger quantity than in the saline constituents of blood. In some pathological conditions there has been observed,* at points where bones and muscles meet, an accumulation of free lactic and phosphoric acids, which has never been perceived at those points in the normal state. The solution and removal of the phosphate of lime, and therefore the disappearance of the bones, is a consequence of this state. It is not improbable that the cause, or one of the causes, of this separation of acid from the substance of the muscle, is this-that the vessels, which contain the fluid of the muscles, have undergone a change, whereby they lose the property of retaining within them the acid fluid they contain. The constant occurrence of chloride of sodium and phosphate of soda in the blood, and that of phosphate of potash and chloride of potassium in the juice of flesh, justifies the assumption that both facts are altogether indispensable for the processes carried on in the blood and in the fluid of the muscles. * Schmidt, Annalen der Chemie und Pharmacie, vol. lxi. p. 329. Proceeding on this assumption, the necessity for Use of salt. adding common salt to the food of many animals is easily explained, as well as the share which that salt takes in the formation of blood, and in the respiratory process. It is a fact, now established by numerous analyses, Inland plants that the ashes of plants, growing at a certain distance from the sea, contain no soda, or only traces of that base. soda, and ride of so The ordinary potashes of inland countries give contain no most convincing proof of this; for they but rarely little chlocontain any carbonate of soda; and when a com- dium. pound of sodium occurs in them, it is not phosphate or sulphate of soda, but chloride of sodium. Wheat, barley, oats, root-crops, and plants with esculent leaves, in the Odenwald, in Saxony, and in Bavaria, contain only salts of potash, without salts of soda; and if, in several, soda sometimes occurs, chlorine is also present, and both are in the proportion to form sea salt. plants in districts In plants growing in maritime countries near the The same sea coast, these proportions are altered. Wheat, maritime pease, and the other leguminous plants, in the contain Netherlands, contain phosphate of potash, and also phosphate of soda, the phosphate of potash, however, always predominating. soda and potash. plants con This is the case even in sea plants, living in a Even sea medium which contains, compared with its amount tain more of soda or sodium, a mere fraction of potash. All soda. sea plants contain much more potash than soda. potash than Necessity of chloride of sodium to animals feeding on inland plants. In respect to these two bases, therefore, the food of animals is not in all places of the same quality or composition. An animal, feeding on plants which contain phosphates of other bases, along with some compound of soda or sodium, produces in its body the phosphate of soda indispensable to the formation of its blood. But an animal, living inland, obtains in the seeds, herbs, roots, and tubers which it consumes, only salts of potash. It can produce, from the phosphates of lime and magnesia, by decomposition with the salts of potash, only phosphate of potash, the chief inorganic constituent of its flesh; but no phosphate of soda, which is a compound never absent in its blood. Whence, therefore, does it obtain this phosphate of soda? The true answer to this question is Action of given by a study of the action of phosphate of potash on chloride of sodium. Phosphate of potash, with 2 atoms of potash (tribasic phosphate of potash, with 2 atoms of fixed base and 1 atom of water) = P0.2K 0, is deliquescent, hardly crystallisHOP phosphate of potash on chloride of sodium. PO 5 able, and has a very feeble alkaline reaction. When we supersaturate phosphoric acid (tribasic) with potash, and evaporate to crystallisation, a salt is deposited, which has an acid reaction -PO 5 ΚΟΙ 2 HOJ There is no salt which loses half the amount of base it contains so easily as the phosphate of potash. If phosphoric acid be neutralised with potash, and chloride of sodium added to the solution, and the whole left to spontaneous evaporation, a phosphate crystallises, which contains both Na O potash and soda (the tribasic salt PO, KO HO while chloride of potassium is found in the mother liquid. It is obvious, that phosphate of potash is decomposed when in contact with chloride of sodium ; part of the potassium combines with the chlorine, while the sodium replaces it in the phosphate, phosphate of soda being produced.* In this way we can understand the formation of phosphate of soda in the body of an animal, which obtains in its food, along with phosphate of potash, or earthy phosphates and salts of potash, no compound of soda except chloride of sodium; and when, in inland countries, the food does not contain common salt enough to produce the phosphate of soda necessary for the formation of the blood, then more salt must be added to the food. From the common salt is produced, in this case, by mutual decomposi * It is evident that the tribasic salt above mentioned, Na O PO, KO may equally well be represented as a double salt, H O composed of phosphate of soda and phosphate of potash. KO 2 POK O = PO, {2NaO} +PO, {20} Na O H O. но HOS W. G. |