presence. Carelessly placed in an uncovered vessel under the bed, particles of down, hairs from the blanket or counterpane are very likely to fall into the Urine, while every time the room is swept a vast number of other bodies, comprehended under the term "dust," are sure to make their way into the vessel containing it, which is also the acknowledged receptacle for every species of rubbish which requires to be got rid of. The practitioner will not be surprised at the multitude of strange bodies he will meet with in the deposit which is collected for microscopical examination. Though much trouble and difficulty would be saved if the ingress of these was prevented by carefully covering the fluid; yet as it is practically impossible to enforce this precaution in all instances, the observer must guard himself against the possibility of being led into error from such a cause.

In a work devoted to the practical examination of Urinary deposits and their recognition as a means of diagnosis, it seems desirable that the characters of some of the extraneous matters most commonly met with, should be first given, so that the observer may at once guard himself against the possibility of mistake.

The fragments of hair delineated in Plate I are liable to be mistaken for portions of casts. Their higher refractive power, and consequent greater thickness of outline, the markings on the surface caused by the arrangement of the imbricated scales upon the surface of the hair, and the projecting edges of the latter frequently seen in profile at the margins, their firmness and hardness, the striated appearance visible in the human hair, and the peculiar disposition of the internal part of the hair in the case of the cat and many of the lower animals, are some of the points which will enable us to distinguish them from casts of the uriniferous tubes. At the same time, the observer should rather depend upon that general idea which he forms from examining these structures fre

PLATE III.

EXTRANEOUS MATTERS COMMONLY FOUND AMONGST
URINARY DEPOSITS.

Fig. 12. Air bubbles.

Fig. 13. Free oil globules.-Oil which has fallen into Urine accidentally, is to be distinguished from oil contained in cells or in casts found in Urine in cases of fatty degeneration of the kidney. Plate XIV, fig. 2.

Fig. 14. Portions of feather.-The knotted pieces represented, are obtained from the lower part of the Ishaft of the feather.

Fig. 15. Fibres of deal swept from the floor. These are very liable to be mistaken for casts. The round pores characteristic of the fibres of coniferous trees, might very readily be mistaken for epithelium. They are, however, distinguished by the irregularity of their outline, by the very regular arrangement of the pores, and by their refractive power.

Fig. 16. Cotton fibres.-A very small fibre in the lower part of the figure, is seen to be twisted round a larger one. Cotton fibres are distinguished by their flattened form, and by the cross markings in the central part of the fibre.

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quently, for enabling him to recognize these bodies with certainty, than upon characters which may be expressed in words. All practically acquainted with such subjects, feel, that every observer must educate his own eye, and render himself familiar with the general characters of the several objects with which it is desirable he should be well acquainted, and which he ought to be able to recognize at a glance.

Flax fibres are known by their jointed structure and slightly fibrous nature.

Fragments of tea leaves can hardly be mistaken for any other structures; the dark appearance of the cells, their large size, and the number of spiral vessels which are connected with the fragments, distinguish them from other substances.

Wheat starch, Potato starch, and Rice starch are readily distinguished from each other. The grains of the first are perfectly circular, of the second egg-shaped, while those of the third are very minute, and of irregular form. The different characters which starch granules present, when examined in air, fluid, or Canada balsam, should be observed.

The starch granules in bread are usually found much swollen and very transparent. Sometimes they appear cracked, but usually they preserve their general form, as represented in fig. 10. Bread crumbs are very commonly found amongst urinary deposits.

The characters of air bubbles and oil globules should be very carefully observed.

Oil globules, when they occur free, as represented in fig. 13, are generally present from accident. They may be derived from an oiled catheter which has lately been passed, from the accidental presence of butter, or from the admixture of milk.