Pus in small quantity, and mucus in excess, whether from the bladder, or, in females, from the vagina, are each of them sources of perplexity which the microscope readily explains. It is of very little consequence which name is applied, as there is evidently no clear line of demarcation between them: very large epithelium scales serve to show that the vagina is the source of the secretion ; of s smaller size, their presence in unusual number might be taken as evidence that the accompanying globules came from the bladder, and not the kidney, and were rather mucus than pus. When the globules are very numerous we cease to call them mucus under any circumstances ; an irregular serrated edge seems to belong especially to scrofulous pus ; little agglomera tions of globules show that there is a tendency to fusion, the urine is scarcely acid, and the source of the secretion is very probably the bladder. Mucus and bladder-epithelium are chiefly found when crystals of uric acid or oxalate of lime are present in the urine, which no doubt acts as irritants on the mucous membrane.
Tubular casts should always be looked for by the student, because they teach him when albumen is dependent on degeneration of the kidney, and thus give him clearer notions of its origin, and of the cases in which its presence is caused by other circumstances : but it would be very rash to say there was no renal disease simply because casts were not seen.
Vibriones and spermatozoa are both causes of opalescence which the micro scope can alone clear up. Chemically, it may be determined that the condition is not one of much importance with reference to disease of the kidney; but spermatozoa are of considerable moment with reference to the general health of thepatient.
Oxalate of lime, as a discovery of late years, received at one time a greater share of attention than it deserved : its presence is by no means rare, and is not in any way connected with perverted function or diseased action of the kidney. It is not uncommonly found in a dumb-bell shaped crystal ; but the student ought not to take this form as characteristic of oxalate of lime, unless the ordinary octohedra be also present.
Uric acid, when found in the urine in crystals, seems to show a different condition of health from that in which it is found only in combination with alkali, and hence the importance of the observation. Probably, when the urates appear as semi-crystalline rounded masses, they show an approach to the same diathesis ; but at present we cannot assign any very satisfactory reason why this substance appears sometimes in the crystalline, and sometimes in the amorphous form—uncombined, or as a compound body. It is worth
remembering that the globular urates occasionally possess so high a refractive power as to have been mistaken for oil-globules.
It is equally difficult to say why the phosphate of lime is sometimes crystal lized, sometimes amorphous : the form of its crystals is long and acicular, and, when present, there can be no doubt that the urine was passed in an alkaline state, and that the alkalescence was not derived from excess of am monia ; but, on the other hand, such a condition of urine does not necessarily imply crystalline phosphate. Triple phosphate, in a large proportion of cases, follows decomposition of the urine; but it is recorded as having occurred when there was no trace of decomposition, and the alkalescence of the urine depended only on conditions of depressed vitality. It is one of those objects which from its unmistakable appearance is of great use to the learner, because it never occurs along with s deposit of urates, but always with the phosphate of lime.
§ 5. Urine free from Deposit.—W We next proceed to apply our chemical tests to the urine which has been decanted off the sedi ment, or to urine which has not let fall any appreciable deposit. Two abnormal ingredients occupy the first place, because they are constantly found in certain conditions of disease, and, as they are freely soluble, give no other direct indications of their pre sence; and a few words must be added on excess of urea, which also never occurs as sediment.
a. Albumen.—The means resorted to for ascertaining the pre sence of albumen are heat and nitric acid, each of which has the property of coagulating it; and in certain cases the extraordinary amount of the precipitate formed by either, leaves no possible doubt as to the fact. It is only where the quantity is small that there is any difficulty in coming to a determination upon the sub ject., and especially when the urine is not quite transparent. In speaking of this opacity (§3), it was shown to be chiefly produced by an admixture of pus or mucus, or an effusion of blood ; and if these circumstances can be traced to disease of the kidney, it is evident that the accompanying albumen will be in considerable amount and the reaction decided. When therefore any doubt exists, the very inconclusiveness of the experiment may, to a certain extent, be regarded as a proof that the kidneys are not diseased.