Notes on the lectures of Prof. John Guintéras on general and special pathology, delivered before the second and third year students of the University of Pennsylvania

Preface

T N response to a frequently expressed desire on the part of the

students, we have undertaken the publication of this volume of notes. During its preparation we have been stimulated by the interest and encouragement of Professor Guiteras, to whom we beg to acknowledge our grateful indebtedness.

We are under obligations to Dr. Alfred Stengel for the cuts of many of the illustrations.

By the kind permission of Dr. Joseph McFarland we have been able to add an epitome of his lectures on Bacteriology.

We hope that the notes will assist the student in mastering the important subject of Pathology.

Chapter I

Pathology is that branch of the science of medicine which concerns itself with the study of the manifestations of energy and the changes in structure which take place in a diseased living being. Broadly speaking, it is the science of disease.

The term "disease" includes all those disturbances of the normal manifestations of life which impair, more or less, the adaptability of the individual to surrounding media.

By " a disease" we understand a group of such modifications occurring with sufficient regularity of association to constitute a distinct species.

Disease adds no new element to the body ; it merely modifies previously existing functions and structures. We deal, therefore, in pathology with two factors : the changes in the function, i. e. f the manifestations of energy, and the changes in the structure, of diseased organs or tissues.

The first recognizable change is one affecting the structure. But we cannot conceive of such a change occurring without some antecedent force or cause to bring it about. This fundamental cause is believed to be certain obscure functional derangements which lead to modifications of structure, and these, in turn, to secondary changes of function. The last become recognizable to us as the symptoms of the disease.

DIVISIONS OF PATHOLOGY.

Analogous to the division of Biology into Morphology, Physiology, and Embryology, Pathology is divided into Morbid Anatomy, or the study of the changes of structure in disease, Morbid Physiology, the study of the changes of function in disease, and Etiology, the study of the causation of disease. Of these three branches morbid anatomy is the most

• 5 advanced ; etiology is also highly developed, chiefly through the impetus which bacteriology has given to it ; morbid physiology, probably the' most important branch, is still very obscure. Pathology may be further divided into

GENERAL AND SPECIAL PATHOLOGY.

In general pathology we study disease from a general point of view ; we study those changes of function and structure that can occur in any organ, e.g., inflammation. In special pathology we study these changes as they occur in special organs, e. g., pneumonia.

GENERAL PATHOLOGY.

Morbid processes are of two kinds : (a) Elementary or Simple — those in which the changes in the tissues are of one kind only, or those occurring in individual cells, e.g., fatty degeneration. They are the elements of which disease is made up.

(b) Compound — those composed of several elementary morbid processes ; e.g., inflammation.

Morbid processes may be integrating or progressive, those in which there is a building up of tissue, or disintegrading or retrograde, those in which tissues are destroyed. The former are exemplified by hypertrophy and hyperemia, the latter by atrophy and degenerations.

SIMPLE MORBID PROCESSES.

HYPERTROPHY.

Hypertrophy is an increase in the size of a tissue or organ, taking place independently of the general growth of the organism and without any marked alteration in the outline of the organ.

Normal Example. — Enlargement of the uterus during pregnancy.

Hypertrophy may be (i) general, affecting several parts of the body, or (2) local, limited to a single organ or part. Local hypertrophy is classified into (a) true or functional hypertrophy, and (b) false or pseudo-hypertrophy.

HYPERTROPHY. 7

True hypertrophy is a uniform enlargement of an organ affecting all the tissues, and is accompanied by an exaltation of function. It is caused by an increased functional demand upon the part, either directly, as in the uterus in pregnancy, or indirectly, when the demand on the organ is the result of the imperfect action of another, usually of a companion organ, as in hypertrophy of a kidney after the removal of its fellow, or the enlargement of one lung when the other is diseased. In false hypertrophy the tissue most apt to be increased is that least concerned in the function of the organ, i. e. t connective tissue. Hypertrophic cirrhosis of the liver, and pseudo-hypertrophic muscular paralysis are examples.

Morbid Anatomy. — In true hypertrophy the outline of the organ is generally preserved; in false hypertrophy it is apt to undergo some change, owing to the presence of an excess of connective tissue.

Hypertrophy is divided into (1) simple, or that in which there is an increase in the size of the individual cells, and (2) numerical, that in which there is an increase in the number of cells. The latter is the more common form, although both very frequently occur together. Simple hypertrophy is not easily demonstrated : we see it best in the pregnant uterus and in the hypertrophied heart.

The term hyperplasia is used as a synonym of numerical hypertrophy ; it implies a multiplication of cells with a tendency to form new tissue. It does not necessarily lead to hypertrophy; indeed, it may cause atrophy, as in atrophic cirrhosis of the liver.

The subject of numerical hypertrophy brings up the question as to the manner in which cell-proliferation takes place. It occurs in one of two ways — (1) by direct cell-division, or amitosis, or (2) by indirect cell-division, mitosis, karyomitosis, or karyokinesis. The latter is the more frequent and more important mode, and depends upon complicated changes in the filamentary substance of the nucleus. This substance is known as mitome, or, on account of the readiness with which it takes up the nuclear stains, hematoxylin, safranin, gentian-violet, etc., as chromatin. The inter-filamentary substance, staining poorly, is termed achromatin.

The threads of the mitome are arranged in the form of Ushaped loops, the closed ends of which are all directed toward the same pole of the nucleus.

From these primary loops delicate secondary filaments are given off, which by their interlacing produce a dense, compact network.

The essential changes preparatory to cell division take place in the loops. The process is usually divided into three stages :

1. Concentration — the thickening of the primary and disap" pearance of the secondary filaments.

2. Splitting of the filaments in their longitudinal axis.

3. Rearrangement of the filaments — (a) Monaster, or motherstar, (b) Diaster, or daughter-star.

At rest. First stage. Second stage. a Third stage, b

When these changes are completed the cell protoplasm and the nucleus become constricted ; division then takes place, leaving two independent cells, each with its nucleus. Special methods ot preparation of tissues are necessary to show the appearances just described. The most important point is to " fix " the tissues as quickly as possible. For this purpose the pieces should be very fresh, should not exceed one-half c. cm. in size, and should immediately be immersed in a good fixing fluid, the best being Flemming's solution: 1 per-cent sol. chromic acid, 15 parts; 2 per-cent sol. osmic acid, 4 parts ; glacial acetic acid, 1 part. The tissue is left in this six to forty-eight hours ; it is then washed in running water three to six hours, and finally hardened in alcohol and imbedded.

The sections are stained for from one to twenty-four hours in a one per-cent watery solution of safranin ; they are then briefly washed in water and differentiated in absolute alcohol containing a few drops of a one per-cent solution of hydrochloric acid in alcohol. When clouds of color cease to be given off the section is removed to absolute alcohol, thence to oil, and mounted.

Under the microscope the nuclei undergoing karyokinetic changes are stained a dark reddish-brown, while the quiescent nuclei are light in color. The most striking appearance is the daughter-star

ATROPHY. 9

Clinical Causes. I . Increased functional activity.

2. Congenital tendency, e. g., giant growth of certain parts.

3. Removal of pressure. The growth of certain structures is kept within bounds by the pressure of adjacent organs. We commonly find increased thickness of the skull in cases where parts of the brain are absent.

4. Direct stimtdation, taking the form of intermittent pressure ; e. g., corns. Constant pressure leads to atrophy.

5. Disturbances of nutrition, (a) Direct disturbances (trophic) of innervation, as thickening of the skin in some nerve lesions. (b) Interference with the function of certain obscure organs, viz., the thyroid gland, the thymus, the pituitary body, and probably the suprarenal capsules.

There is a disease known as Acromegaly \ which is characterized by an enlargement of the extremities, chiefly the hands, and of the face. Both the bony and the soft parts are involved. In a number of cases the disease was associated with pathologic changes in the pituitary body.

ATROPHY.

Atrophy is a diminution in the bulk of one or more of the component parts of an organ. Since the more important tissueelements are usually affected, there is also a diminution of functional activity. Normal examples are the atrophy of the thymus gland in early life ; of the umbilical blood-vessels after birth ; and of the female reproductive organs at the menopause. There may be smallness of size not due to atrophy. For example, an organ may be diminutive from an arrest of development, a condition termed hypoplasia. It is seen in chlorosis, in which we frequently find that the sexual organs and the heart and great vessels are abnormally small. Total absence of an organ or a part of an organ is called aplasia or agenesis ; it gives rise to monstrosities.

Morbid Physiology. — Atrophy is brought about either by an insufficiency in the food supply of the cells, or by an inability on the part of the cells to use the nutritive material brought to them. It is (a) simple, due to a diminution in the size of the cells, without marked change in their protoplasm, or (b) degenerative, due to a breaking down of the protoplasm of the cells.

Morbid Anatomy. — (a) Macroscopy. An atrophic organ is smaller; its outline is usually retained, although the surface maybe io NOTES ON PATHOLOGY.

irregular; the consistency is, as a rule, greater than normal, on account of a relative or absolute increase of the connective tissue ; its color is darker, from a relative excess of pigment ; frequently, too, new pigment is deposited, (b) Microscopy. The cells are diminished in size or degenerated ; the connective tissue is increased.

Brown Atrophy occurs in organs the seat of chronic congestion, especially in the heart and liver.

Clinical Causes. — I. Senile changes. — These are to a certain extent physiologic ; are pathologic when occurring early. They affect especially the testicle, heart and lungs (senile emphysema).

2. Defective nutrition.

(a) General, as in starvation.

(3) Local deficiency of blood-supply, as from obstruction of an artery.

3. Constant pressure, as atrophy of bones from pressure of an aneurysm.

4. Disuse, as atrophy of muscles in ankylosis of a joint.

5. Disturbances of innervation. Neuropathic atrophy. This is due to a loss of the trophic influence and is most strikingly exemplified by the atrophy of the muscles in acute anterior poliomyelitis, or infantile palsy, a disease affecting the ganglion cells of the anterior horns of the spinal cord. It is a degenerative atrophy.

INFILTRATIONS AND DEGENERATIONS.

Both imply retrograde changes in the cells, infiltration being the lowest one in the series of disintegrating processes. It consists in the deposit in the cell of an abnormal substance or of a normal constituent in excess. The nucleus and cell-protoplasm are pushed to one side and generally preserve their integrity. Degeneration is the conversion of the cell-protoplasm into an abnormal substance. It is a more serious process since it destroys the cell.

The infiltrations are : Fatty, calcareous, pigmentary, serous, and glycogenic.

FATTY INFILTRATION.

This consists in the storage of excessive quantities of fat within the cell, the protoplasm remaining relatively intact.

Normal examples are the adipose tissue and the liver. Pathologically, it occurs in the subcutaneous tissue, where, if general,

FATTY INFILTRATION. n

it is termed obesity or polysarcia ; in the liver, in the heart, around atrophic organs, etc. In obesity certain parts, as the eyelids, the alae nasi, the lobules of the ears, the lips, and the prepuce escape. Histologically, the fatty deposit affects both the cells and the intercellular substance, the red corpuscles and the ganglion cells of the nervous system being alone exempt.

Morbid Physiology*. — There exists in fatty infiltration a disturbance of the fat-building and fat-storing functions. The deposit of fat may be due to an excess of food ingested or to an impairment in the consumption of the fat normally brought to cell. Defective oxidation is at the bottom of the process.

All food-stuffs, fats, albuminoids, and carbohydrates may give origin to the deposit of fat, particularly the last-named.

The albuminous food may be converted into fat within the body ; thus, the cow which consumes but little fat produces a large quantity of it out of the vegetable proteids. Certain post-mortem changes also illustrate the derivation of fat from albuminous substances ; adipocere, a fatty material, may be formed out of the muscles after death.

Animals fed on carbohydrates deposit fat. Bees produce wax out of the plant-sugar upon which they feed. How this conversion is brought about within the body is not known.

Morbid Anatomy. — (a) Macroscopy. The size of the organ is increased, but the outline is preserved ; the consistency is usually diminished, yet it may not be greatly altered ; the color is yellowish, either uniformly or in streaks, the latter being the case especially in the heart. The surface of section shows minute fat droplets, and the knife used is oil-stained.

(b) Microscopy. Primarily the fat is deposited in small granules, which have a tendency to run together to form large rounded droplets, possessing a light center and a dark contour, or vice versa, depending on the manner of focusing. The protoplasm and nucleus are pushed to one side. The latter retains its structure and can be seen distinctly unless covered by the fat-droplet. In fatty degeneration the tendency of the fat-granules to run together is exceptional.

Fatty infiltration may be selective, affecting particular parts of an organ. In the heart, for instance, it is found in the connective tissue between the muscle fibers, and beneath the pericardium. In the liver it is especially marked toward the periphery of the acini, where the portal vein deposits the fat coming from the digestive tract. Chemically, the fat of fatty infiltration is the same as that found in the body normally, namely, a mixture of the neutral fats, stearin, palmatin, and olein.

In the horse olein predominates, the fat therefore is soft and yellow ; in cattle the harder and whiter stearin is chiefly found.

After death, and in certain pathologic states, such as gangrene and other degenerations, during life, the fat may take on a crystalline form, the crystals being needle-shaped, the so-called margaric-acid crystals, or in large rhombic ia) choiesterin, {b) Fat- plates, each with a corner cut out, constituting CryS, 1;J;L C cr 0U ° d the cholesterin-plates.

Clinical Causes. — I. Heredity. This is the important factor in general obesity.

2. Disturbed digestion. This may cause chemical changes favoring the deposit of fat ; generally, however, it is associated with an excessive appetite.

3. Lack of exej-cise. Not only does deficient physical exercise conduce to fatty infiltration, but also lessened mental activity, as is seen in certain forms of insanity. In fattening animals it is customary to restrict their exercise to the lowest limit by confinement.

4. Anemia, probably by lessening oxidation-processes. We may have an extensive deposit of fat in chlorosis. The fattening of animals for slaughter may be hastened by one or two bleedings.

5. Alcohol. The ingestion of alcohol, especially in the form of malt-liquors, favors the deposit of fat either by increasing the consumption of food or by diminishing oxidation.

6. Local disturbances of circulation interfering with the proper nutrition of a part.

CALCAREOUS INFILTRATION OR CALCIFICATION.

Calcification is the deposition in the tissues of earthy salts, principally the carbonates and phosphates ot calcium and magnesium.

Physiologic example. The deposit of salts in bone. The salts of pathologic calcification do not differ from those deposited in health.

CALCAREOUS INFILTRATION OR CALCIFICATION. 13

The term ossification should never be used as synonymous with calcification. Calcification is only a step in the process of ossification.

Pathologic Seats] 1. The tissues that normally tend to undergo calcification, as cartilage.

2. The connective tissues in general, particularly those ot the blood-vessels.

3. Tumors.

4. Foreign bodies, as dead parasites {Trichina Spiralis).

5. Old inflammatory foci.

6. Thrombi and emboli, especially in veins (Phleboliths).

7. Ganglion cells of the nervous system and epithelial cells.

8. Certain cavities, as that of the gall-bladder, of the urinary bladder, and of the intestines. The deposits here take the form of concretions or stones, the composition of which varies. They are as a rule not made up of earthy salts.

True calcification affects tissues the blood supply of which is poor. Cartilage, for example, possesses no capillaries, and its cells are separated very widely from one another.

Morbid Physiology. — (a) There may be an excess of earthy salts in the blood, a condition present in osteomalacia. The salts are removed from the bones and deposited in other tissues. (Metastatic calcification.)

(b) In other cases the calcification can only be explained by ascribing it to defective nutrition.

Morbid Anatomy. — We meet calcareous infiltration :

1. In plates — especially in tissues arranged in layers, as in the dura mater, the serous membranes of thorax and abdomen, the intima of blood-vessels.

2. In granules, which may be microscopic in size or larger. The organ preserves its outline, the surface of section is gritty.

3. In spicules and needles, as in the brain, extending in various directions, especially near the surface of the organ.

Microscopy. Both the cells and the intercellular substance are affected. In connective tissue, the intercellular substance, in epithelium, the cells are first affected. The cell-body becomes granular ; the nucleus is concealed by the granules and remains unstained. If the process is intense, the cells appear black and their outline is obscured.

There is in some pathologic processes an attempt at ossification, but the new bone is imperfect.

It differs from normal bone in several ways.

i. The cells are not arranged in whirls around a central vessel.

2. There is no formation of regular plates around canals.

3. The intercellular substance is stained by hematoxylin, while that of normal bone is not.

Reactions and Tests. The mineral acids dissolve the granules with effervescence and the liberation of C0 2 . The granules are insoluble in ether and in alcohol, and are thereby distinguished from fat-granules.

Clinical Causes. — 1. Osteomalacia and other diseases breaking down bony tissue.

2. Old age. Here the circulatory system is especially selected by the infiltration.

3. Defective circulation.

4. Poisons, especially corrosive sublimate. The manner in which poisons produce calcification is not well understood. They may cause anemia of the tissues. In HgCl 2 poisoning, the deposit occurs especially in the renal epithelium. Bismuth and aloin act similarly.

5. In cavities, from a chemical change in the fluids whereby the salts are precipitated from solution.

In gout, sodium urate and also the carbonate and phosphate are deposited, this deposit occurring almost exclusively in the connective tissues, especially that of joints and tendons (Tophi).

The deposit occurs in the form of fine granules in the cells and the intercellular substance. As the disease progresses large masses or minute needles may be produced, the latter having the peculiarity that they run parallel with the fibers of the tendons. The urate salts are soluble in mineral acids, with the production of crystals of uric acid.

PIGMENTARY INFILTRATION.

This consists in the deposit of abnormal quantities of pigment in the tissues.

Normal seats. The red blood-corpuscles, the skin, the choroid coat of the eye, the hair, etc.

Morbid Physiology.— The pigment may be introduced from without, external, or may be formed within the body, internal

PIGMENTARY INFILTRATION. 15

pigmentation. The latter is again divided into (a) hematogenous and (b) metabolic pigments. Hematogenous pigments are those derived from the coloring matter of the blood ; they are either hemoglobin or derivatives of it. The metabolic pigment is elaborated out of the albuminates of the cells themselves ; or it may be brought to the pigmented parts by wandering connective tissue cells.

The pigment of the rete mucosum is of metabolic origin. '

Hematogenous Pigmentation.— The hematogenous pigments are hemoglobin, hemosiderin, hematoidin, biliary pigment, and ferrous sulphid. The pigmentation occurs in one of two ways :

(a) The pigment may stain the tissues in a soluble form, in other words, it may be hemoglobin. The first tissue to be stained is the blood — hemoglobinemia. In severe degrees of this condition, the hemoglobin also colors the urine — hemoglobinuria. Hemoglobinemia is met with in some of the infectious diseases, as pyemia, and in malaria; after the injection of certain poisons; sometimes after the transfusion of serum from one animal to another.

(b) The pigment may be deposited in an insoluble form, being a decomposition-product of hemoglobin. The insoluble pigments are hemosiderin — a dark, granular pigment, containing iron — and hematoidin, a brownish pigment, occurring in rhombic crystals, not containing iron. The form which the insoluble pigment takes depends to some extent upon the activity of the tissues the seat of pigmentation. Where active cell-processes are going on, hemosiderin is produced ; where this is not the case, hematoidin will be formed. In old hemorrhagic foci in the brain, we find hemosiderin at the periphery, hematoidin in the center.

Melanosis is a general tendency to the formation of abnormal blood-pigments, which appear as minute granules in the blood itself or in organs. It occurs chiefly in malaria, where the pigment may be so abundant, particularly in the pernicious varieties of the fever, as to cause capillary emboli. These are met with especially in the brain. The pigment of melanosis may be devoid of iron ; it then resembles melanin ; sometimes it contains iron. The malarial pigment is generally free from iron.

Note. — The student should observe that the term melanosis has nothing to do with the metabolic pigment melanin ; it signifies the deposition of altered blood-pigment. The word originated at a time when the differentiation of the various pigments had as yet not been attempted.

Morbid Anatomy. — We find the insoluble pigments in bruises — here chiefly as hemosiderin — and in hemorrhages in the interior of organs. In the latter instance the pigment is apt to remain for a long time, assuming often a bluish or slate color, as in the intestines after an attack of dysentery.

Tests for blood-pigment. To a watery solution of the bloodstain add tincture of guaiac; a white or whitish-red precipitate is produced which turns blue on the addition of an ethereal solution of hydrogen dioxid. The blue precipitate may be dissolved out with alcohol. (A/men's Test.) This test is very characteristic.

The spectroscopic test, which is absolutely positive. The spectrum of hemoglobin (i. e. oxy-hemoglobin), consists of two dark bands, one at the junction of the yellow and green, the other in the middle of the green. Non-oxidized hemoglobin presents a single band, which may be considered to be the result of the union of the two oxy-hemoglobin bands. It is, however, smaller than the combined width of these two bands. Methemoglobin gives rise to three dark bands, the two characteristic of oxy-hemoglobin, with an additional one in the orange.

Bile-pigmentation : Jaundice , or Icterus. Since bile is elaborated exclusively by the liver, the origin of jaundice must always be hepatogenous. It may, however, arise in one of two ways : (a) from simple obstruction of the bile-ducts ; (J?) from excessive formation of bile-pigment, this generally occurring when there is an exaggerated destruction of blood-coloring matter. It is the latter form to which some clinicians give the name of hematogenous jaundice.

Tests. Bile-pigment is insoluble in water and in alcohol ; it is soluble in chloroform, and gives a pretty play of color with nitrous acid or nitric acid containing nitrous acid fumes. {Gmelin-Heintz' Test)

Ferrous sulphid, FeS. This results from the action of hydrogen sulphid on the iron contained in the hemoglobin. It is seen post-mortem in the abdominal walls and peritoneum, as a diffuse bluish discoloration.

Metabolic Pigmentation.— The pigment— called melanin — is elaborated out of the protoplasm of the cells, without the intervention of blood-pigment. It occurs normally in the skin^ the choroid, in hair, etc. Its composition is variable — sometimes it contains iron, at others it does not. Sulphur is generally present.

SEROUS INFILTRATION. DROPSY. 17

Pathologic occurrences, (a) Addison's disease. The chief characteristic of this is the bronzing of the skin, due to an excessive deposit of melanin. The majority of cases are associated with disease of the suprarenal capsules.

(5) Tumors — as melanotic sarcoma, or melanoma.

(c) In degenerations of muscles, as in the heart, particularly in atrophy.

Tests. Melanin is as a rule soluble in boiling acids, and in boiling KOH ; also in boiling alcohol. Sometimes it is insoluble.

■ External Pigments. — I. Bacterial pigments— as in blue pus, the color of which is due to the bacillus pyocyaneus.

2. Silver — which may be deposited during the medicinal administration of silver salts. The pigment discolors the skin, producing the condition termed Argyria.

3. Coal dust, especially in the lungs — Anthracosis. When the pigmentary deposit is excessive, it leads to chronic fibroid changes.

4. Iron-dust. Siderosis.

5. Stone-dust. Calcicosis.

6. Tattoo-pigment. This is found also in the lymphatic glands nearest to the tattooed area.

7. Lead. The blue line on the gums.

SEROUS INFILTRATION. DROPSY.

This consists in the infiltration of the tissues with diluted lymph.

Pathologic seats. (1) Serous cavities. (2) Loose areolar connective tissue. (3) Lungs. (4) Epithelium — here it is probably of a different character, resembling more a degeneration.

Morbid Physiology. Serous infiltration may be brought about in various ways. (1) Through obstruction of the lymphatics and veins. Being the result of mechanical influences, the dropsy under these conditions appears first in the dependent parts, as in the lower limb, and in the lower portions of the pleural and peritoneal cavities. (2) Through a change in the composition of the blood, as in anemia. Weakness of the vessel-walls may contribute to the production of the infiltration. (3) Through changes in metabolism. The healthy state of the organism depends upon the normal character of the interchange constantly going on between the tissues and the blood. This interchange is not merely the result of a mechanical transudation ; it is an active process. If disturbed at j 8 NOTES ON PATHOLOGY.

any point, disease develops, at one time serous infiltration, at another, as we shall see later, inflammation. (4) Through changes in the walls of the blood-vessels : {a) over-distension (b) disease of the vessel-walls.

Character of the Fluid. It has the same composition as the lymph, but contains more water and less corpuscular elements. From inflammatory fluid, which it resembles, it is distinguished by being less inspissated. Its specific gravity does not exceed 1016, and its proportion of albumin is less than three per-cent. Inflammatory fluid is denser and contains more albumin.

Morbid Anatomy — (a) Macroscopy. The part, as a limb, is swollen, pale, somewhat translucent in appearance, pits on pressure, and has a lower temperature than the same part in health. In the case of the lung, we find that the organ is enlarged and on section oozes a frothy serum.

Different terms are employed, according to the seat of the effusion :

1. Anasarca. When the general subcutaneous connective tissue is infiltrated.

2. Edema is applied to the infiltration of the subcutaneous tissues and the internal organs, as edema of the lungs. Edema ot the brain is in reality edema of the membranes, the pia-arachnoid.

3. Hydropericardium, hydrothorax, and ascites refer to serous effusion into the pericardial, pleural, and abdominal cavities respectively.

(b) Microscopy. The fluid infiltrates the intercellular substance and separates the cells widely from each other ; the fibrils of the intercellular substance are swollen and also widely separated. These features are seen best in fresh tissues.

In epithelium the process is really a degeneration ; it occurs principally in catarrhal and other inflammations of mucous membranes ; it is also observed in the muscle of the heart. In the case of mucous membranes the cells are large and filled with fluid ; they lose their shape and appear dropsical. Clear vacuoles, free from the granules found in the protoplasm, are present. In the heart the serous degeneration gives rise to the semblance of cavities within the muscular fibers.

Clinical Causes. — 1. Valvular Heart Disease. The dropsy begins in the feet.

GLYCOGENIC INFILTRATION. 19

2. Diseases of the liver ; especially cirrhosis, which causes obstruction of the portal circulation, and this in turn ascites.

3. Diseases of the kidney. Here several factors are active in the production of the serous infiltration — (a) changes in metabolism, (b) changes in the composition of the blood, and (c) changes in the walls of the blood-vessels. The edema begins, as a rule, in the loose areolar tissue of the eyelids. It may be noticed quite early in the finger-tips, from the swinging of the hands in walking.

4. Cachectic states, as in tuberculosis and cancer. The edema in cachexia depends upon changes in the composition of the blood and upon a feeble state of the heart.