Health consists in a natural and proper condition and proportion in the functions and structures of the several parts of which the body is composed. The standard of health is not, however, the same in all individuals; that which may be health to one may be disease to another. Thus: the healthy pulse in adults averages from 70 to 80; yet there are some in whom 90 or 100 is a healthy pulse. Some persons fatten on a quantity of food on which others would starve. The animal functions, muscular strength and activity, nervous sensibility, and the sensorial powers, vary still more in different individuals, yet all within the limits of health.

Causes of disease are those circumstances which essentially precede it, and to the operation of which its occurrence is due. In many instances these circumstances elude our observation. In many others, the true cause, if apparent, is combined with other antecedent circumstances which have no share in producing the disease, and yet are liable to be mistaken for causes. These circumstances are to be sifted, and the true cause discovered, only by the attentive observation of large numbers of cases in which disease is produced. Thus, it was long a matter of doubt whether the Itch could be engendered from filth, as well as from contagion; but, since microscopic investigation has discovered the existence of the Itch-mite, no doubt remains that this insect is the only essential cause of the disease.

The causes or circumstances inducing disease may be intrinsic, or existing within the body; or they may be extrinsic, having their origin without the body. Extrinsic causes are very numerous; comprising all the agencies which can act upon the body or mind, such as temperature, air, moisture, food, poisons, mechanical and chemical influences, sensual impressions, etc, etc.

But the common causes of disease are seldom of a decided and positive character; they are often present without disease ensuing and they are known to be causes only because disease is observed to ensue in a greater number of cases when they are present than when they are absent. Thus, improper food is a cause of indigestion, and exposure to cold is a cause of catarrh; yet many persons eat unwholesome food without suffering from indigestion, and many are exposed to cold without taking cold. But those who do suffer from indigestion observe that they do so more after taking improper food; and those who are afflicted with catarrh can often trace it to exposure to cold. In some cases, however, where the predisposition to disease is sufficiently strong, it may, under certain circumstances, become in itself a sufficient cause of disease; thus, a person with a very weak stomach always has indigestion. So, likewise, exciting causes, if sufficiently strong, may produce disease without predisposition; thus, a person not predisposed to indigestion, may be pretty sure to get it, if he takes a sufficient quantity of fat, raw cucumber, or any such indigestible matter. Take another example. A healthy person, living in a marshy district, may not get Ague until he becomes debilitated from any cause, such as cold or fatigue; then the poison will act. But, without his being thus weakened, if the exciting cause be made stronger by his sleeping on the very marshy ground itself, then the poison may act without predisposition.

Predisposing causes of disease may be divided into:

Debilitating Influences,

Excitement,

Previous Disease,

Present Disease,

Hereditary Constitution,

Temperament,

Age,

Sex,'

Occupation.

Debilitating causes of Predisposition are the most numerous of any; as we might expect from the fact that constitutional strength generally implies power of resisting disease.

These causes may be classed as imperfect nourishment; impure air; excessive exertion of body or mind; want of exercise or sedentary habits generally; long continued heat; long continued cold; habitual intemperance with intoxicating liquors; depressing passions of the mind, such as fear, grief, and despondency.

Many are the instances in which numbers, as well as individuals, have escaped a prevalent disease, until depressed by some unhappy event or apprehension, and then they have fallen victims. It is a common remark, that when a contagious or epidemic disease prevails, those who take most precautions frequently suffer, because they arc timid and fearful, whilst the stout-hearted and reckless escape. During the first Cholera in England, the Medical Officer of a Government Establishment, situated in a healthy part of the country, (himself an old Army Surgeon), had a terrible dread of getting Cholera; he made up his mind that if it came in the neighborhood he should take it, and, if he took it he should die. He took every precaution in his power to preserve the health of his own immediate vicinity, but, at length, one day he got some fish that disagreed with him, made up his mind at once that he had got Cholera and should die; and he did die, although there was not another case within miles of the place.

Excessive and repeated evacuations, either of the blood or of some secretion. Previous debilitating diseases.

Excitement

Excitement in many cases, or rather over-excitement, is apt to lead to mischief. Violent exertion makes the muscles or their fasciae peculiarly liable to rheumatic inflammation from the subsequent action of cold and damp. Excessive indulgence in a stimulant diuretic beverage, such as punch, renders the kidneys liable to inflammation or congestion on exposure to cold.

Previous Disease

There are many diseases by which a person is more liable to be attacked after having had them once. Thus, a child who has once had croup is very liable to a return. Convulsive disorders, such as Chorea, Hysteria, and Epilepsy are extremely apt to recur; and the longer they have existed, the more difficult they are to remove, and the more ready they are to reappear on the application of any exciting cause. Rheumatism, Gout, Gravel, many cutaneous diseases, Dropsy, Jaundice, and many others are of this class.