Urinary deposits may be preserved either in the dry way, in Canada balsam, turpentine, oil, and similar fluids, or in aqueous solutions. Only large crystals of the oxalate of lime, lithic acid, and some of the phosphates and lithates, can be preserved in the dry way. Dr. Beale gives the following directions for the preservation of urinary deposits: "After the crystals have been allowed to collect at the bottom of a conical glass vessel, the clear supernatant fluid is to be poured off, and the crystals are to be washed with a little dilute alcohol, or with a very weak solution of acetic acid. When the process of washing has been repeated two or three times, a small quantity of the deposit is to be transferred by means of a pipette to a glass slide, and the greater part of the fluid soaked up with a small piece of blotting paper. The crystals are next to be spread a little over the glass with the aid of a fine needle, in order to separate the individual crystals from each other; and the slide is to be placed in a warm place, or in the sun, until quite dry; but care must be taken that the drying is not carried on too rapidly, and that too great a degree of heat is not employed. A narrow rim of paper, or cardboard, is next to be gummed on the slide so as to include the crystals in a sort of shallow cell; and lastly, the glass cover is to be put on and kept in its place either by anointing the edges with a little gum-water, or by pasting it down with narrow strips of paper, which may be variously arranged and ornamented according to taste.

"If the crystals of lithic acid are to be mounted in Canada balsam, they should be carefully dried first, as above directed, and afterwards over sulphuric acid, and then moistened with a small drop of spirits of turpentine. The slide is now to be slightly warmed, in order to volatilize the greater part of the turpentine, and a drop of Canada balsam is to be dropped upon the preparation from the end of a wire, which may be readily effected by holding the wire with the balsam over the lamp or hot brass plate for a minute or two in order to soften it. The slide is next to be held over a lamp, in order to keep the balsam fluid until any air-bubbles which may be present have collected into one spot on the surface of the liquid balsam, an operation which is expedited by gently moving the slide from side to side. The air-bubbles may now be removed by touching them with a fine-pointed wire. Lastly, the glass cover is to be taken up with a pair of forceps, slightly warmed over a lamp, and one edge is allowed to touch the balsam. The surface is permitted to fall gradually upon the balsam, so that it is wetted by it regularly, and only by very slow degrees, for otherwise air-bubbles would yet be included in the preparation. The glass slide with the preparation may now be set aside to cool."

There are many substances, however, which cannot be preserved to advantage in Canada balsam, or by the dry method. Such are epithelium, casts, torulæ, confervæ, fat-cells, pus, mucus, . Such substances should be placed in shallow glass-cells,

&c.

and covered with aqueous solutions, varying in character and strength to suit the specimen. The best preservative fluids are weak spirit, glycerine diluted with water, solutions of gelatine, creasote, naphtha, &c. The gelatine solution answers very well for the preservation of dumb-bell crystals of oxalate of lime, while the creasote and naphtha solutions are better adapted for the preservation of epithelium, tubular casts, &c. Crystals of the triple phosphate are best kept in aqueous solutions of ammonia; for cystine dilute acetic acid answers very well.

Vomited matters consist of articles of food variously altered by the digestive processes, epithelium and mucus from the mouth, fauces, pharynx, oesophagus, and stomach, gastric juice, bile, and the various matters generated in disease. As different portions of vomit contain different ingredients, small portions taken from points considerably separated, should successively be subjected to examination. The various transitions which alimentary substances undergo in the stomach, must often necessarily render the determination of the exact composition of the vomited matters a point of extreme difficulty.

FIG. 423.

Starch-granules are often met with in abundance, but sometimes so changed as to require the addition of tincture of iodine to detect them. Fig. 423 represents the appearance of starch corpuscles after partial digestion in the stomach. The epithelium is also frequently found to be more or less altered from endosmosis, and partial digestion. Vibriones and various species of torule are also observed in vomit. The sarcina ventriculi, a peculiar fungus discovered by Mr. Goodsir, in matters ejected from the stomach, has also been observed in the fæces, in the urine, and in an abscess of the lung. The fluid of waterbrash consists mainly of epithelial scales and small oil-globules. In the rice-water vomit of cholera patients numerous flocculi of epithelial cells are found. The coffee-ground vomit appears to consist mainly of the coloring matter of the blood reduced to a finely granular state and mingled with disintegrated blood-corpuscles. The sediment deposited by the black-vomit of yellow fever upon standing, in all probability is chiefly composed of blood-globules in various stages of disintegration. The epithelial cells of this fluid "vary in respect to their abundance, size, and shape, and while stated by some to have presented themselves in all the specimens examined, they have, in some instances, been found wanting. Of the six specimens reported upon by Dr. Leidy, two were deficient in this particular. The size and shape of these cells, as observed by Dr. Riddell, have already been referred to. In the hands of Dr. Michel, the scaly, columnar, and spheroidal, have, at different times, been plainly made out with their nuclei

and nucleoli, but in very different proportions-the scaly or lamellar cells being always most numerous."

FIG. 424.

Uterine and Vaginal Discharges present quite different characters in different specimens. The examination should be instituted as soon after they are collected as possible, and without the addition of water, as this may affect the natural appearance of the constituent elements. Epithelial cells and blood-globules in varying quantities compose the menstrual discharge. In leucorrhoea many of the epithelial cells are filled with oil-granules, and mingled to a greater or less extent with pus-corpuscles. Blood-globules are also observed very much altered in shape. (See Fig. 407.) In cancer of the uterus the microscopic examination of the discharges, becomes highly important in arriving at an accurate diagnosis. Cancer-cells, in such cases, may often be detected in the discharges.

When they are broken down or considerably altered in form, not a little difficulty will be experienced in assigning to them their true value. The student should be careful, also, not to confound the columnar epithelium of the ureter, with the spindle-shaped cancer-cells. Fig. 424 represents the microscopic appearances of some cancerous juice squeezed from the uterus; that to the left is the natural appearance, the other after the addition of acetic acid.

SEROUS AND DROPSICAL FLUIDS.

The sedimentary matters should be collected from serous fluids, and examined in the same way as urinary deposits.

An examination of the freshly effused fluid of ascites reveals only a few cells floating in a

clear liquid. In chronic ascites, however, numerous granular and spherical cells, mostly non-nucleated and varying in size, are observed. The sediment consists of delicate fibres, interlaced, and having cells in the meshes or interstices, together with plates of cholesterine. Occasionally blood and pus-corpuscles may also be detected.

FIG. 425.

The hydrocelic fluid consists of some delicate cells, and oilglobules, and occasionally some spermatozoa and plates of cholesterine.

'Dr. R. La Roche on the Nature and Composition of Black Vomit. Amer. Jour. of Med. Sciences, April, 1854.

Cells, oil-globules, free granular måtter, and occasionally bloodcorpuscles and crystals of cholesterine are the principal constituents of the deposit obtained from ovarian fluid. Sometimes masses of gelatinous or colloid matter are mixed with these elements. Minute fibres are sometimes observed crossing each other in various directions, and contain in their meshes thus formed, a transparent jelly filled with round or oval corpuscles. (See Fig. 424.) The cells are either small, transparent, granular, and non-nucleated, or large, opaque, and filled with oil globules. Fig. 376 represents fatty granules, mixed with plates of cholesterine from an ovarian tumor, after Prof. Bennett.

INJECTIONS.

In studying the vascularity of tissues, injected specimens are of great utility. The student should give some attention, therefore, to the practice of injecting the different organized structures which he may desire to examine. Dr. Beale, in his admirable little work on the application of the microscope to clinical medicine-a work of which we have availed ourselves freely in the construction of this chapter-gives the following practical directions as to the time, mode, &c., of making injections.

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Generally, it may be remarked that we should not attempt to inject while the rigor mortis lasts. Many days may in some cases with advantage be allowed to elapse, particularly if the weather is cold, while in warm weather we are compelled to inject soon after death. As a general rule, the more delicate the tissue, and the thinner the vessels, the sooner should the injection be performed. Many of the lower animals, annelids, mollusca, &c., and fishes, should be injected soon after death. In making minute injections of the brain, only a short time should be allowed to elapse after the death of the animal, before the injection is commenced. Injections of the alimentary canal of the higher animals should be performed early-not more than a day or two after.

"Minute injections of the papillæ of skin, particularly of the fingers and toes, cannot be successfully made until the cuticle has become somewhat softened by allowing the preparation to remain in a damp cloth, or to soak in water, for some days. In these situations the vessels are strong, and in their ordinary state, the injection will not traverse them, in consequence of the cuticle preventing their gradual distension by the injecting fluid. A similar plan must be followed in making injections of the tongue, and other parts where the epithelial covering is unusually dense, and firmly adherent to the vascular surface beneath.

"If the subject be a small animal, it is better to take out part of the sternum, and fix the pipe in the aorta. If only part of an animal is to be injected, the largest artery supplying the part should be selected, and all the other open vessels may be tied or stopped with the small forceps.

"A small portion of intestine can be injected by cutting out the corresponding portion of mesentery attached to it; and after searching for a large vessel, all the others may be tied, together with the open ends of the alimentary tube." "A pipe of somewhat smaller diameter than the vessel should be selected, and an opening may then be made in the vessel of sufficient size to admit the pipe, which can now be inserted. The needle, charged with thread or silk, is then carefully passed round the vessel, the thread seized with forceps, and the needle withdrawn over the thread. This operation is sufficiently simple where the vessel is large and strong; but where thin and easily torn, it requires great care. The thread is now tied tightly round the vessel close to the extremity of the pipe, and then attached to the two projecting wires, to prevent the possibility of slipping.

"In injecting from veins a similar method is pursued, taking care to choose a vein in which the valves are not numerous, or in which they are altogether absent. The portal vein can be reached by opening the abdominal cavity, care being taken not to tear any of the branches below the point where the pipe is inserted.

"Greater care is required to fix the pipe in the vessels of fish, in consequence of their being so readily torn. Excellent injections of fish may frequently be made as follows: The tail is cut off with a sharp knife at a short distance posterior to the anus, and if the cut surface be examined the ventral artery may be easily found situated immediately beneath the bodies of the vertebræ. A pipe is carefully introduced and pushed down some distance, so as to prevent the injection from coming out, or the end of the vessel may sometimes be separated from the surrounding parts and tied in the usual way. By this simple proceeding capital injections can often be made very easily.

"Minute injections of the branchiæ of some of the mollusca may often be made by very carefully placing the pipe in the largest vessel that can be found, and slowly injecting. The extreme delicacy of the vessels prevents any attempt being made to tie them to the pipe, and, of course, much injection will be lost. From the large size of the vessels, however, much will run into the capillaries. In this way I have easily succeeded in injecting the branchiæ of the Pinna ingens, and fresh-water mussel (Anodon), both of which form beautiful microscopical objects.

"In order to inject the smaller gasteropods (slugs, snails, &c.), we must pursue a different method. In the muscular foot of these are situated many large lacunæ, or cavities, which communicate with the vascular system, or, in fact, form the vessels which are distributed to this organ. If the injection can be forced into any of these lacunæ, it may be made to traverse the whole vascular system. To introduce the pipe a small hole is made obliquely in the foot, taking care not to force the instrument too far. A small pipe is next inserted, and when the pre