A TEXT-BOOK OF PATHOLOGY.

PART I.

GENERAL PATHOLOGY.

PATHOLOGY is the science that deals with disease in all its aspects. It includes the study of the causes, the manifestations, and the results of disease.

Three important subdivisions of the study of pathology are recognized, viz., etiology, or the study of the causes of disease; morbid or pathologic anatomy, the study of the structural changes in disease; and morbid or pathologic physiology, the study of disturbances of function. In the latter group is included pathologic chemistry, as morbid chemical action and its results are the outcome of disturbed function.

Pathology may be divided into general and special pathology. The former treats of causes of disease and pathologic processes irrespective of any individual part; the latter deals with the causes or processes in individual diseases, organs, or parts.

Disease itself may be defined as abnormality in structure, in function, or in both combined. It is doubtful whether alteration of function can occur without some alteration in structure, but it frequently happens that functional disturbances are present though no structural alterations are discoverable even by the most precise methods of investigation.

The symptoms of disease are the expressions of abnormal functional activity, and are therefore properly discussed under the head of pathologic physiology; but they are so important from a practical standpoint, and form such an extensive subject of investigation, that they are usually considered apart from pathology, in special treatises dealing with diagnosis and the practice of medicine.

CHAPTER I.

THE ETIOLOGY OF DISEASE.

THE causes of disease may be classified as predisposing and determining. The former prepare the system or part by rendering it weaker and less resistant; the latter are the immediate or specific causes of disease.

Predisposing Causes.-The normal system is able to cope with the determining causes of disease to a certain point by its general vitality and regulative functions. Thus heat and cold may prove harmless if not too intense or prolonged. In the case of exposure to heat, the superficial capillaries become dilated, sweating increases, and there is increased heat dissipation from the surface at the same time that increased respiratory function. occasions evaporation and loss of heat through the lungs. In the case of exposure to cold, increased muscular exercise leads to greater heat production, while contraction of the superficial bloodvessels restricts the elimination of heat. When, however, a certain point of intensity is reached in the case of heat, cold, or other causes of disease, the normal organism is unable to oppose sufficient resistance, and disease or injury results. The degree of resistance differs in different individuals, in different races, or people living under varying climatic conditions, etc. In some the degree of resistance may be so great that certain diseases are never contracted. The term immunity (q. v.) is applied to this state. In other persons there is a recognizable weakness of resistance in one direction or another which constitutes a definite predisposition. The latter may be either hereditary or acquired. Acquired predisposition results from previous disease, vices of living, and like

causes.

Heredity as a predisposing factor in disease is probably less important than was formerly believed, but undoubtedly plays a part in many conditions. By hereditary predisposition is designated abnormal weakness of resistance transmitted from the mother or father to the offspring. There may be congenital weakness that is not definitely hereditary, as it is more or less accidental— that is, not the outcome of tendencies of the same kind (latent or active) in the parent. Heredity may be direct or immediatethat is, from the parent (himself or herself presenting the condition) to the offspring-or remote, as in cases in which the hereditary trait is latent in the parent. One or several generations may thus be free from certain diseases or tendencies which reappear in later generations. This return to conditions present in remote ancestors has been likened to atavism in the Darwinian sense. some cases hereditary traits are conveyed from the male parent to the male children, or from the female parent to the female off

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spring; in other cases there is crossed transmission. A peculiar form of heredity is seen in hemophilia and some other diseases, which are transmitted through the female members of a family, who generally remain unaffected, to the male offspring. Hereditary traits sometimes predispose to a number of allied affections. This is particularly striking in the case of the neuropathic heredity, in which various forms of nervous disease may appear alternately or irregularly in members of an affected family.

A number of theories have been constructed to explain the mechanism of heredity. Darwin in his hypothesis of pangenesis suggested that minute particles are given off from all of the cells of the body; these are collected in the reproductive cells, which in consequence represent all of the bodily characteristics, hereditary and acquired. Weismann denied the transmissibility of acquired characteristics, and holds that in the process of reproduction a certain amount of "germ-plasm" passes from the parent cell into the offspring, where it remains, and is in turn passed on to succeeding generations, thus perpetuating ancestral characteristics.

Determining Causes.-Among the immediate or determining causes of disease are those which originate outside the body and those which are generated within the body. Among the former are included traumatism, heat, cold, and other physical agents, poisons, and living organisms, including bacteria and various animal parasites. The causes of disease originating within the body itself are less definitely known, but it has been found in chemical studies that various products of normal metabolism when accumulated in abnormal quantity, or products of disturbed metabolism, may occasion local or widespread disease of various sorts. This self-poisoning is designated auto-intoxication.

The term "auto-intoxication" is frequently applied to poisoning by products of intestinal putrefaction. This application of the term is not, strictly speaking, correct. The same poisons might have been produced by putrefaction of food outside the body, when the use of the name auto-intoxication would be manifestly absurd. If poisons are produced by imperfect digestion, and these affect the organism, the condition could properly be termed auto-intoxication.

TRAUMATISM.

Traumatism, or mechanical injury, may be of various sorts, gradual or sudden, small or large; and the effects are dependent upon the form and severity of the injury. Pressure brought to bear upon a part leads to disturbances of the circulation and more or less direct injury of the cellular elements. When the pressure is gradual true atrophy of the part may occur, as in the case of the atrophic liver resulting from lacing. When the pressure is greater and the circulation is completely arrested more destructive change may result, such as necrosis or gangrene. This is seen in the necrotic atrophy of bone resulting from the pressure of aneurysms,

or the gangrene of extremities resulting from ligation. Wounds. -Frequently, inflammatory reaction occurs in the surrounding tissues when traumatic injuries have been sustained. This is illustrated in all forms of wounds, and it is through the inflammation and subsequent regeneration of tissue that the areas of destruction are restored. In cases of injury by fine particles, as in powder-marks of the skin, or the surface injuries sustained by miners and metal-workers, or in individuals inhaling sharp particles like coal-dust, marble-dust, or steel-filings, small injuries of the tissues result. The foreign bodies may be subsequently discharged, leaving a focus of inflammation, or the inflammation may surround the particle imbedded in the tissue, and encapsulation by fibrous-tissue formation may occur. Large injuries in which the tissues are contused or broken may lead to extensive inflammation, in part the result of the direct injury to the tissues and L part the result of injury of the blood-vessels.

Gross traumatism of the body as a whole, as in falls, crushing injuries, etc., causes various disturbances according to the part mainly involved. Rupture of the viscera, as the lungs, heart, liver, spleen, stomach, or intestines, may occur. When the head is violently struck, unconsciousness is common as a consequence of either disseminated punctiform hemorrhages, large focal hemorrhages, or obscure and possibly only functional disturbances. Commotio cerebri, the condition occurring in such cases, may be fugacious or may lead to permanent disorder dependent upon organic changes in the brain. Spinal symptoms, met with after railway injuries and like accidents, may be due to hemorrhage and secondary morbid processes in the cord, or may be due to the uncertain pathologic conditions constituting hysteria.

PHYSICAL CONDITIONS.

Heat.-High temperatures produce local or general results according to the mode of application and degree of heat.

Local excess of heat produces various lesions. Moderate excess leads to relaxation of the walls of the blood-vessels; with increasing grades of temperature there is in addition necrotic change in the cells of the part, and exudation of serum causes vesicle formation. Still higher grades of temperature produce immediate destruction, perhaps with charring, of large or small areas, while the surrounding tissues suffer from reactive inflammation and hyperemia. Extensive burns involving one-third or more of the surface of the body frequently cause death. In these cases it is likely that poisonous products are formed, either directly through tissue- and blood-destruction, or indirectly through disturbances of the functions of the skin or internal organs. The immediate manner of death is often in the form of shock; when the termi

nation is more delayed various vascular, hemic, and tissue-disturbances may occur. Intravascular coagulation is not unusual, and is not improbably the result of the liberation into the blood of tissue-elements set free in the areas of local destruction, or to substances produced by direct destruction of the blood. The same substances may account for the existence of fever (ferment intoxication). The intravascular coagulation caused in this or other ways may induce venous stasis and localized hemorrhages. Focal necrosis or degeneration of the tissues of various organs, such as the liver, kidneys, or the mucous and serous membranes, may be due to thrombotic occlusion of vessels, or to the influence of circulating poisons without thrombosis, or to both. Duodenal ulcer is often referred to as an occasional result of extensive burns. The blood itself may present evidence of disease in the form of degenerations of the corpuscles, in the reduction of their number and of the amount of coloring matter; while regenerative changes frequently present themselves some time later (nucleated red corpuscles). Changes in the urine may occur in cases of extensive burns, in consequence of the tissue-destruction (hemoglobinuria, albumosuria).

Exposure to general high temperature varies in its effects according to the manner of exposure (dry air, steam, etc.). An animal exposed to a constant temperature somewhat above the usual surrounding temperature presents a slight increase of its bodyheat, which is compensated for by increase in the respirations and pulse-rate. Much higher temperatures may cause death by coagulation of the tissues; notably, the muscular structure of the heart, or the respiratory muscles. Before this extreme is reached, however, it may be found that the consumption of the tissues of the body is greatly in excess, though the respiratory quotient is altered in favor of the amount of air inhaled. Continuous exposure to excessive heat frequently causes peculiar disturbances in man, known as heatstroke, sunstroke, or insolation and heat-exhaustion. In these conditions hyperemia and edema, or even inflammation of the meninges, may occur. These lesions are sometimes supposed to be the result of the direct effect of the heat; but there is reason to believe that they may be occasioned by poisonous substances produced within the body by disturbed metabolism, as a result of the heat.

A portion of the body, as an arm or a leg, may be exposed for a limited time to excessive temperatures (300° to 400° F.) in dry air without injury. The general temperature is slightly elevated, but metabolism is practically unaffected.

The effects of general or local heat are much increased when the organism as a whole or in the part involved is below par. A paralyzed limb is burned or scalded at comparatively low temperatures.