A. Pus corpuscles from an abscess. a. The same after treatment with
acetic acid. B. Mucus corpuscles from the Schneiderian membrane. a.
After a drop of acetic acid has been added. C. Mucus corpuscles speckled
with pigment granules, from a case of chronic irritation of the lining
membrane of the larynx, with expectoration of grey sputa.

Serous Fluid effused into large cavities, as the thorax or abdomen, frequently contains pus cells, and also granular corpuscles, in addition to masses of fibrous material.

Sometimes the fluid from serous cysts will be found, under the microscope, to contain scolices of some hydatid. An echinococcus cyst, for example, occurring in the region of the neck, will be very probably mistaken for a serous abscess until the fluid is evacuated and submitted to minute investigation, when the presence of scolices or fragments of them, or even of some of the hooks, will at once prove the nature of the tumour.

The secretions, and even the blood from whence they are derived, undergo certain changes, the result of disease, and frequently contain abnormal products.

Mucus from the stomach and intestines may contain vegetable organisms, both fungi and algæ. The secretion from the bronchial membrane very frequently includes the ova of entozoa, or even the parasites themselves; pus corpuscles and blood discs are also commonly seen.

Milk. During certain diseased states, the mammary gland will contain blood discs, pus corpuscles, and granular corpuscles, which must not be confounded with colostrum corpuscles, normally present in the fluid immediately after parturition, as represented in fig. 162, p. 176.

Urine, more than any other secretion, requires the aid of the microscope for the detection of the numerous abnormal products which it frequently contains.

In the limited space assigned to this portion of the course it would be impossible to include the necessary directions for the microscopic and chemical examination of the secretion, but a few of the more common forms of urinary deposits are depicted for the guidance of the student in the course of his investigations.

Urinary Deposits.

One of the most frequent deposits in urine is the uric acid, the crystals of which occur most commonly as shown in the next illustration. For the detection of this deposit the low power is generally sufficient, as the crystals are large, sometimes perceptible to the naked eye.

Fig. 164.

CRYSTALS OF URIC ACID.

Another not uncommon deposit is oxalate of lime, which occurs in two forms; the octahedral crystal, which is most characteristic, and the dumb-bell crystal, which is also one of the forms in which carbonate of lime occurs in the urine of the horse. The illustration shows both these forms of crystal from human urine.

Oxalate of lime from urine.-Magnified 200 times.

The triple phosphates are at once to be recognised by the presence, under the microscope, of large prisms like those shown in the next drawing.

Fig. 166.

Crystals of triple phosphate.-Magnified 200 diameters.

Besides crystalline deposits there are organic products, which are frequently found in the urine, for instance, fat, fibrinous casts of the uriniferous tubes, blood, pus, and, occasionally, the ova of

entozoa.

The accompanying drawing represents a number of tube casts with cylindrical epithelium and a few crystals of oxalate of lime.

Fig. 167.

Urinary deposits from a case of organic disease of the kidneys. 1. Tube
casts. 2. Cylindrical epithelium. A few crystals of oxalate of lime, with
a quantity of amorphous matter, are also depicted.

Blood. Besides the crystalline bodies described at p. 48, blood may contain other microscopic elements, whose presence in abundance may be important, for example, an excess of white corpuscles, which would be readily detected. Ova of entozoa may be discovered, and at once suggest the presence of parasites in some parts of the organism from whence the fluid has been procured.

Sometimes minute organisms are observed moving with extraordinary rapidity. These are termed bacteria and vibrines.

Bacteria are found in splenic blood of animals that have died from splenic apoplexy. Under the high power they appear as minute jointed filaments possessing great facility of motion.

Vibrines are common in fluids undergoing decomposition; they may be compared to minute chains, exceedingly flexible in their movements. Some species are not longer than the 300th of a line, and the 3000th of a line in thickness.

CONCRETIONS.

As it occasionally happens that the student, in the course of his investigations, meets with substances in various parts of the body differing in their nature from any of the elements hitherto described, it may be well to mention that a great variety of concretions are to be met with in the animal body, their nature varying with the locality in which they are found, their form depending upon the peculiar conditions in which they are placed. Thus, when a concretion occurs singly it is usually spherical, oval, or elongated; when numbers occur together they are cubical, pentagonal, hexagonal, or polygonal, according to the amount and direction of the attrition or pressure which they exert on each other during the movements of the viscera in which they are contained. Even foreign bodies, introduced into the internal cavities, undergo alterations of form from the operation of the same causes, as was illustrated some time ago in the case of a bullock whose rumen was found, after death, to contain fourteen large leaden bullets, every one of which had lost its spherical form, and become polygonal. Again, in the case of foreign substances that have accidentally found their way into the human bladder, portions of catheter, sealing wax, &c., are always found, after a time, to be moulded into peculiar shapes by the movements of the bladder.

Concretions occur in the liver, kidneys, bladder, salivary ducts, stomach, and intestines.

Biliary Calculi.-These are, perhaps, among the most common; they are usually of a greenish-yellow colour, but sometimes they may be of a dark yellow, brownish, or even black colour; occasionally specimens are met with nearly white. They vary in size from that of a pin's head to a hen's egg, the average being the size of an ordinary marble.

Biliary concretions consist, for the most part, of cholesterine, in different degrees of purity. The purer the specimen, the more crystalline will be the fracture, and the lighter the colour. They often show a concentric arrangement of layers, crossed by striæ running from the centre to the circumference, as seen in the drawing.