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Scope and Terms of Pathology.—“ Pathology is that subdivision of biology that has for its object the study of life in its abnormal relations." It is the study of diseased conditions, and aims at the discovery of the changes of organization and function that result from all abnormal conditions.

Health exists when the normally constructed body properly performs its functions. Disease is any variation from this normal standard, and may be described as any condition in which the organism finds itself in abnormal relationship with its environment. Disease is, therefore, a general term signifying any variation from the normal condition. A disease is a condition characterized by the occurrence of definite phenomena and constituting a recognized type of abnormality. Thus, fever is a diseased state or condition found in many different diseases. Typhoid fever, a febrile affection with definite symptomatology, is a disease.

In the scope of pathology are included the source, progress, changes, and terminations of disease. A knowledge of pathology forms the only rational foundation upon which the art of medicine can rest, as it is through its teachings alone that symptoms can be understood and treatment properly applied. The chief contrast between the medical art of the ancients and of the semi-civilized nations and modern medical science is the ignorance of pathology on the one hand, and an increasing knowledge of it on the other. Until our knowledge of biology in its normal and abnormal relations is perfected, medicine cannot become an exact science.

It is customary to divide the subject into General Pathology, that deals with disease processes common to the whole organism, as fever, cachexia, degeneration, etc., and Special Pathology, in which the diseased conditions of the special organs are considered.

Morbid Anatomy, Morbid Histology, and Morbid Physiology, or, as they are frequently called, Pathologic Anatomy, Histology, and Physiology, contemplate respectively the gross and minute structural and functional changes.

Nosology, or the Classification of Disease.—Diseases are variously classified according to the standpoint from which they are viewed. Thus, they are spoken of as hereditary, if actually derived from one or both parents ; congenital, if appearing at birth, but not necessarily referable to the parents; and acquireit

, if appearing subsequent to birth. According to their time of occurrence, diseases are also described as infantile in babyhood, and senile in old age.

According to their origin, certain diseases are described as symotic, infretious, or specific, when they depend upon living entities, such as bacteria, protozoa, insects, worms, etc. Some of these diseases that can be communicated by touch are called contagious. Miasmatic diseases were formerly supposed to depend upon certain deleterious influences exerted by the soil; at present no true miasmatic disease is known.

According to their manner of occurrence, diseases are described as sporadic, when isolated cases occur at irregular intervals; epidemii, when large numbers occur at the same time ; endemic, when a disease is continuously present in a community; and pandemic, when everywhere, in all countries, nearly everybody is more or less influenced by a disease.

Toxic diseases depend for their origin upon the presence of poisonous substances, either derived from external sources or manufactured in the body, either by parasites or by its own metabolic processes abnormally carried on.

According to their lesions, diseases are described as organic and functional : organic diseases being characterized by definite lesions of the organs and tissues ; functional diseases having no discoverable lesions, and manifesting themselves only by disturbed physiologic action. Organic diseases are anatomic, functional diseases physiologic in character.

The distribution of disease makes it either local or general. Constitutional diseases are general diseases whose hold upon the organism is such as to affect its very constitution or functional organization.

The duration of disease is variable, so that all morbid processes can be classified as acute or chronic.

Acute diseases are of abrupt onset, active symptomatology, and short duration. Chronic diseases, on the other hand, are of insidious onset, mild symptomatology, protracted duration, and progressive lesions. Subacute affections are neither acute nor chronic, but often begin as acute diseases, running protracted courses and healing slowly.

Ephemeral or fugacious diseases are acute processes of exceedingly short duration. Continued fever is of protracted duration.

With advancing knowledge the number of diseases for which it is impossible to find an adequate cause has greatly diminished, but, unfortunately, the term idiopathic is still employed to describe them.

Diseases with recognizable causes are known as symptomic.

According to their occurrence, diseases are described as primary, secondary, tertiary, and recurrent.

A primary disease is the first occurrence or expression of disease. A secondary disease depends upon some primary disease. Tertiary disease is seen in syphilis, and refers to the third set of symptoms of that affection.

Diseases also vary in their tendencies. Some are benignthat is, tend to recover without materially injuring the patient; while others are malignant, and tend toward his final destruction. A few diseases are called fulminant, because of the extreme rapidity and severity of their symptoms.

Recurrent diseases are characterized by a tendency to recur or come back, as in the case of malignant tumors. Recurrent fevers are called relapsing.

Intercurrent affections develop during the course of some other disease, as when a person suffering from tuberculosis of the lungs is attacked by pneumonia and dies of it before the tuberculosis had become sufficiently far advanced to endanger life. The pneumonia is then described as intercurrent.

The structural changes wrought by disease are known as lesions. They may be initial or primary, secondary, or tertiary.

Nosogeny, or the Development and Progress of Disease. It is best considered in relation to certain of the specific febrile affections, in describing which all of the employed terms are used. These affections result from the presence of parasitic bacteria which enter the body, producing what is called the infection. For a time subsequently they increase in numbers and elaborate metabolic products that shall be the cause of subsequent changes. This period is, therefore, a latent one, during which development is going on, and is known as the period of incubation. During it vague symptoms are not infrequent, but are indefinite and not very severe ; they are called prodromes. The recognized disease is not infrequently ushered in by definite symptoms that may be slow and insidious, or abrupt or explosive, and constitute what is known as the invasion or onset. The disease now pursues a course that for some time may be without much variation, constituting what might be termed the period of active disease, and is called the acme or fastigium. Subsequently comes a period of decline, that marks the beginning of recovery, followed by a more or less rapid gain of strength and return to the normal state during convalescence.

The time of infection may pass unnoticed ; or, on the other hand, may be referred to some particular moment, as when some wound, accidentally or intentionally inflicted, was the point of entrance of the disease-producing germs.

The period of incubation is very variable, depending upon the ability of the micro-organism to bring about its effects. Septic infections may develop in a few hours. Tetanus, or lockjaw, has an incubation period of from three to ten days ; hydrophobia, one that is said to vary from weeks to months.

The onset or invasion varies with each disease. Pneumonia has a sudden invasion, characterized by a chill, followed by cough, dyspnea,etc. In typhoid fever there is a progressive slow increase of temperature, lasting over a number of days, the temperature each evening being about a degree higher than in the morning. The exanthematous fevers of childhood are frequently ushered in by reflex symptoms, such as vomiting, headache, and convulsions.

The fastigium also varies, some diseases scarcely developing before their decline begins; others, as typhoid fever, continuing for one or two weeks. When the fastigium is without marked alterations, it is said to be continuous, as in typhoid fever. In the malarial fevers extraordinary fluctuations are observed, the high fever being interrupted by intermissions, during which the temperature returns to the normal ; or remissions, during which it falls below its customary altitude, but not to the normal. Sometimes the course of a disease is marked by occasional paroxysms or exacerbations, during which all the symptoms may become greatly exaggerated or renewed, or entirely new symptoms develop, as in the course of tetanus, with the tonic spasm of trismus for a constant symptom, and clonic spasms with opisthotonos at intervals.

The period of decline is not without interest, for, while the greater number of diseases end by a gradual amelioration of all the symptoms, or lysis, a few are characterized by a sudden disappearance of the serious symptoms and immediate improvement, this being known as crisis.

Convalescence is brief or protracted according to the extent of the damage to be repaired. Sometimes during convalescence the symptoms all reappear, and a relapse or repetition of the disease, usually less severe than the original affection, makes its appearance. There may be several relapses, and patients who have successfully passed through the disease may die in the relapse. Any exacerbation of disease, as well as a relapse, may be described as a recrudescence.

The termination of disease may be in a more or less complete return to health, or recovery, as in most of the acute affections, or in death. Incomplete recovery also sometimes occurs, producing a chronic or indefinite continuance of the morbid process. After recovery from a disease, other diseased conditions depending upon conditions set up by the original process may appear. These are secondary diseases or sequelu. Thus, after diphtheria it is common for paralysis of certain groups of muscles to occur from toxic injury to the nerves. In diphtheria and typhoid fever remote abscesses sometimes result from the entrance of pyogenic bacteria into the blood from the lesions of the disease. After pleurisy and pericarditis fibrous adhesions may deform the chest and embarrass the circulatory and respiratory functions. Peritoneal adhesions following peritonitis may lead to obstruction of the intestines and to death. The sequelæ of disease are, therefore, important, serious, and sometimes themselves fatal.


THE ETIOLOGY OF DISEASE. To define disease as an inharmonious relation of the individual to his environment is sufficient to suggest what multitudinous factors have to be considered under the head of etiology. The individual may be congenitally deficient in parts and unable properly to perform his functions; or he may inherit from his parents certain vices that pervert his nutrition and cause fatal weakness; or he may accidentally lose important members and miss their absent functions ; or he may become the host of parasites which absorb his nourishment, poison him with their products, or transform his tissues into useless perversions; or he may become intoxicated through extrinsic poisons taken in the air, food, or water; or his metabolism may become defective and he may succumb to poisons generated within his own body. Add to these the rigors of climate, the fury of the elements, the feebleness of youth and the miseries of old age, and it will be seen that the “ devils by which we may be possessed can truly be called legion."

The factors involved in the etiology of disease may be divided into intrinsic and extrinsic.

I. INTRINSIC FACTORS IN THE ETIOLOGY OF DISEASE. Heredity.—This term is much misused in medicine, being applied to many prenatal conditions that have nothing to do with it in the true biologic


In biology the term heredity is used to describe conditions transferred from parent to offspring through peculiarities of the germ plasm. It does not refer to accidental conditions of prenatal life by which the health or perfection of the offspring is affected..

It has not been determined through what means the hereditary transmission of peculiarities--especially acquired peculiarities—takes place. All theories thus far suggested fail to explain the phenomena.

Biologists differ as to whether acquired characteristics can be transmitted to offspring or not. If not, then there cannot be such a thing as a hereditary disease or deformity.

Lamarck and Darwin believed firmly in inheritance and in the transmission of acquired characteristics, and Darwin made it the basis of his theory of evolution. Weissmann, and perhaps a majority of the biologists of the present day, doubt or disbelieve its possibility. It seems certain that experimental characteristics are not transmitted-i. e., mutilations such as result from circumcision, amputations, scolisectomy, etc., are not transmitted, but it appears certain that spontaneously acquired variations from the normal may be transmitted.

Adami has suggested that heredity may be explained upon the assumption that the idioplasm, or that part of the protoplasm possessing vital properties, is composed of a mass of molecules which form a central ring, to which side rings may be attached or from which they may be detached without alteration of the central primitive ring. Environment causes the central

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