-SALINE PRECIPITATES.
The various secreted fluids may be regarded as saline solutions, in which the proportion of menstruum and of dissolved salts is chemically accurate. If any cause affect this proportion in such manner as to lower the ratio of solvent fluid, precipitation of the solid matter must follow ; or if some new substance be introduced which changes the chemical relations of the dissolved and dissolving materials, a similar result necessarily ensues. The alteration of ratio referred to may obviously arise either from diminution of the solvent, or increase of the solid, material. Thelatter of these states exists at the moment of secretion ; the former may either exist then, or be induced subsequently to the act of secretion (in consequence generally of unnatural stagnation of the fluid in its ex cretory' passages) by evaporation, by absorp tion, possibly by exosmosis, and other agencies.
But embracing in one view all the saline products found in the body, nothing can be more certain than that a primary modification in the qualities of the secretions themselves is the main agent in their generation. No point in general pathology affords matter of more curious inquiry than the causation of these changes in the character of the secretions. If in some cases observation teaches us to refer thern to a local morbid power, limited in dura tion as in the extent of surface it implicates, in other and much more numerous instances they may be traced to the operation of a con stitutional influence, itself dependent on diet, mode of life, climate, &c.
Products belonging to this sub-class present themselves in the form of § 1. Crystalline or amorphous particles ; § 2. Masses.
§ 1. Custalline or amorphous Al though in the great majority of cases these particles are, as just explained, simple inor ganic precipitates from the secretions,yet recent inquiries have distinctly shown that they are in some instances associated with organic mat-, ter, which retains the form of the saline parti cles after these have been dissolved away by acids. Now in respect of the mode of associa tion of the inorganic and organic materials under these circumstances, there are three possible cases. (1.) The organic matter may simply adhere to the surface of the saline in gredients. (2.) Salts of crystalline form may lie in the interior of an organic cell, closely embraced by its wall. Otoliths are each of them, as shown by Krieger*, enclosed in a membranous vesicle. (3.) What .appears to be the crystalline form of the saline matter may, in truth, be simply an accidental result of its association with organic particles, to which the form observed in reality belongs.
Crystallisation of inorganic matter arises in the hutnan body under various conditions,— either after death or during life ; and in the latter case as a natural occurrence, or as a morbid phenomenon. Crystals of these kinds are microscopical objects.
The fmces contain crystals naturally ; in ty phoid fever with morbid change in Peyer's glands, crystals appear to form in much greater abundance than under any other circum stances : in this disease, too, they are found heaped up near the implicated glands, instead of being scattered through the contents of the bowel ; and are said, unlike those of ordinary fxces, to be readily soluble in sulphuric and hydrochloric acids without effervescence.
Crystals discoverable during life in connec tion with acknowledged states of disease may be provisionally arranged as follows — Of the natural secretions which (in conse quence of alteration in their composition) are liable to contain saline matters in the form of minute crystals, the urine is by far the most important. With the strictly crystalline variety may be associated certain amorphous pulveru lent precipitates. These products occur in the urine in the form of pellicle, cloud, or sedi ment ; in other words, they form a thin stra tum on the surface of the fluid, float between the upper and lower surfaces, or gravitate:to the bottom of the containing vessel. These varying positions, appreciable to _the naked eye, aid the observer in forming a rough esti mate of the nature of the saline matter, and may be almost conclusive on the point. The microscopical and chemical characters com bined supply, however, the real evidence from which their composition is ascertained* ; in order to avoid repetition, we will defer the consideration of these characters until engaged with the subject of urinary calculi. We shall have occasion to recur, in describing the mor bid substances (b, c, d), referred to in the above classification, to the appearance of crystals within them. But it may be stated here, as a general fact, that as the materials of all such crystals exist primarily in solution, and as absorption, evaporation, or chemical appropriation of water leads to their deposi tion in the crystalline form, there is a source of fallacy in the examination of preparations kept in spirits ; certain salts, combined with the aqueous part of the material examined, are deprived of their water by the alcohol, and separate in crystalline forms.
2. ilfasses. — Adventitious products be longing to the present sub-class, and possess ing sufficient bulk to be called masses, form an important group, divisible into two series differing from each other in a variety of im portant natural characters. Some of them are, in truth, composed wholly or essentially of saline or other non-plastic materials, precipi tated from the fluids of the system ; others of similar materials, deposited in an adventitious basis, itself stromal or non-stromal. In the first series, the non-plastic compounds form the essential, if not the whole, " materies morbi ;" in the second, these compounds are merely superadded to pre-existing matter (com monly morbid) of another kind ; and such superaddition, instead of increasing the ac tivity of functional disturbance in the system, tends frequently to weaken the destructive influence of that pre-existing matter. For the sake of convenience, bodies belonging to the first series may be termed true cakuli, or sim ply calculi ; to the second, pseudo-eakuli, or concretions.