DISEASE. Disease is a lack or absence of ease; a condition of uneasiness or of pain. Pathologically, it is a collection of phenomena occurring constantly during life and after death, according to Savile; Huxley defined it as perturbation of the normal activities of a liv ing body." Foster conceives of it as °Any de parture from, failure in or perversion of normal physiological action in the material constitution or functional integrity of the living organism?) It is a condition resulting from dis ordered physiological action and recognized by change in structure or in altered function. The area of altered anatomical structure, or the tissue changed through, for example, circula tory or eliminative failure, is called a lesion. The term disorder was formerly given to a group of symptoms without a discoverable anatomical lesion; but disorder and disease are now used as synonymous terms. Briefly and conveniently, then, disease is a departure from health, recognized during life through symp toms and physical signs.
Symptoms are subjective manifestations ex perienced by the patient, as for example, pain or buzzing in the ears. Physical signs are objective manifestations, discoverable by the physician on examination, such as heart mur murs or waves caused by fluid in the abdominal cavity or anomalies of pupils.
In the olden time before chemistry, biology and bacteriology had been developed, disease was regarded as a dynamic entity, which in vaded tissue, causing changes, and with a certain train of symptoms, and was so de scribed, together with its cause and diagnosis, in the old °systematic Through the elaboration of experimental methods, the new school of pathology has been established and normal physiological processes, as well as the processes of the agencies resulting in disease, have become more thoroughly understood and definite causes have been confidently assigned.
Classification of An old classifi cation divided diseases into diatketic, or those which are dependent upon a constitutional pre disposition, or diathesis (q.v.), and enthetic, or those which arise from invading external causes. An example of the few diathetic dis eases is haemophilia (q.v.). This is a consti
tutional disease generally hereditary and charac terized by frequent and prolonged haemorrhages from very slight wounds, or from spontaneous rupture of blood vessels in the mucous or serous membranes. There is a greatly lessened plasticity to the blood and a degeneration of the coats of the blood vessels. Examples of enthetic diseases are plumbism (lead poisoning) and typhoid fever; the former caused by ab sorbing lead in solution in water run through lead pipes or from fresh paint; the latter caused by swallowing in food or water the typhoid bacillus.
Some make two divisions for purposes of classification : germ diseases and non-germ dis eases, or infectious and non-infectious diseases. Germ diseases are caused by entrance into and growth within the body of bacteria (q.v.), which are vegetable spores. (See DISEASE, GERM THEORY or). Many harmless bacteria naturally exist in the intestines; but most of the fatal diseases, including pneumonia, typhoid fever, tuberculosis, cholera and bubonic plague, are due to the entrance of the specific bacteria in each case.
Another classification, now little used, di vides disease into organic and functional, the former being those in which tissue changes are demonstrated in the viscus or organ affected; while in the latter the organ fails to functionate properly, although itself exhibiting no lesion. But in functional diseases there are always dis tant lesions, owing to which, through reflex or directly conducted nerve action, functional disorder occurs.
Diseases are also classified as idiopathic, if arising from causes developed within the body; traumatic, if resulting from wounds or injuries; acute, if of sudden invasion and pursuing a brief, definite course; chronic, if pursuing a long course and persistent; contagious, if com municated from person to person; constitu tional, if pervading the whole system, as blood poisoning; local, if limited to a small area, as a boil; congenital, if existing before birth; nervous, if attacking some part of the cerebro spinal system or the nerves; syntotic, if due to the action of ferments.