pointment here too as to the transmission of desired qualities and the correction of observed defects. These irregularities, while they embarrass us in our reasonings, afford us, however, ground of vague hope in individual instances, and are therefore recited here. I only add one remark, that nature not unfrequently passes over, we know not why, one generation or more in the hereditary communication of predispositions. So the salpa, we are told, exhibits identical peculiarities in alternate generations; and still stranger, the cercaria offers us a similar regular succession in alternate fives; that is, the first five generations differ each from every other, but resemble the next five in regular progression: the 1st and 6th, the 2d and 7th, the 3d and 8th, and

so on.

3. Predisposition of race or tribe must next be spoken of. National characteristics are, of course, in a certain sense hereditary, but their origin is of wider and more varied extent than can be included under the head of mere parental descent. Color is the most natural dividing line of the races, but its influence, if it exert any, is so mingled with other agencies that it is but vaguely understood. The white man everywhere exhibits a more ready proclivity to periodical fevers and other diseases derived from what we call malaria, and dies of them in larger proportion than the colored tribes. These are all susceptible specially of the exanthemata, and yield to their attack. The Red Indian melts away before smallpox; the Polynesian disappears under the milder infliction of rubeola. The black is liable to tetanus and cholera, which are comparatively fatal to him.

Temperaments seem to me, when at all pronounced, to be rather topics of pathological than physiological discussion. They constitute modes of predisposition, the result of hereditary and tribal peculiarities. Though their importance has been exaggerated, and the description of them greatly intensified, they are truly worthy of our attention as manifesting tendencies or proclivities which should be watched and appreciated. Thus, in the sanguineous temperament we have depicted a notable activity of the circulation with peculiar facility in the process of sanguification. Hence arises a particular liability to inflammations and other maladies, of which hyperemia is a part, or which depend upon the force or momentum with which the blood is propelled, as apoplexy, hemorrhage, &c.

In the phlegmatic, we have a condition of the vascular system contrasted with the above. Blood is made slowly and imperfectly, and circulates quietly and languidly. There are torpor and sluggishness of assimilation, nutrition, and secretion, with consequent liability to glandular obstructions, morbid deposits, and transudation from the atonic capillaries. The Dane and the Hollander may be indicated as offering examples of the physiognomical and pathological contrast thus described.

The nervous temperament, sometimes also entitled the poetic and the melancholic, is characterized, as these phrases import, by inordinate susceptibility of the sensorial system-the brain and nerves. The senses are acute; the faculties of the mind rather keen and active than strong or well balanced; the imagination especially lively. These

qualities imply great mobility and excitability, physical, intellectual, and moral. The functional movements of all the organs are readily modified and disturbed. Spasmodic and convulsive affections promptly follow any mode of irritation. The spirits are easily elated and depressed. Hallucinations, eagerly admitted and warmly entertained, run into many varieties of insanity; while the restless and eager desire of excitement soon brings fatigue, satiety, ennui, and despair in its train. It is chiefly from this temperament that the unblest grave of the suicide is filled.

We must not omit to observe that these several temperamentsthe constitutional peculiarities referred to under that comprehensive word-run into and mingle with each other, so as to be found usually combined and complicated, seldom absolutely simple. In like manner the individual peculiarities to which they give rise will be multiplied, varied, and modified in a definite relation with the diversities of structure and conformation with which they are indissolubly connected.

Of acquired predispositions we may distinguish the normal and the morbid, the transient and the permanent. Many of these are incidental to our modes of life, our habits, our avocations. All classes and grades of men, all trades and professions have their besetting maladies, invited by the states of system engendered and built up. The diseases of the civilized man, setting aside exposure to exciting causes, would differ from those of the savage; the manner of living of the gentleman predisposes him to some diseases not likely to affect the artisan, and protects him from the tendency to others. Students are more liable to cerebral disorders; hard labor, while it develops muscular strength, gives liability to rheumatism; it is everywhere the working classes that suffer most from cholera, typhoid fevers, and indeed all epidemics.

Of all transient predispositions, sleep is the most deserving of our study. Its relation to various maladies varies exceedingly, and is often deeply interesting. Sleep is the correlative of sensibility, the psychical action, as death is the correlative of life, the organic action. Death implies destructive change; sleep, restorative change. Yet it is curious to observe that its immediate causes are such as tend to impair and injure the organism, and its proximate cause, or the condition which determines it and in which it may be said to consist, is scarcely distinguishable from disease. Two elements seem to be always present in sleep; a vascular congestion, giving intravascular pressure upon the brain, and a collapse or passive state-the opposite of erethism or tension-of the cerebral fibres. Thus we seem to understand why apoplexy and epilepsy so often come on during sleep. The tendency is aided doubtless by the recumbent posture indulged in. Marshall Hall advises that the epileptic should not be allowed to sleep soundly at any time. I have noticed in some of my patients a special liability to a paroxysm at the moment of waking; just when the brain may be supposed to be arousing itself to a state of activity from its repose. But we have not yet explained why croup and asthma assail us during the first hours of sleep, and the terrible spas

modic dyspnoea of hydrothorax; nor why cholera, and diarrhoea and colic, attack when we have slept some time, or just at early morning; nor why the vomiting of the pregnant woman is most troublesome just upon waking.

Contrasted with these facts, let us remark that malarious fevers rarely, if ever, commence their attack during sleep. I have never read nor heard of the first paroxysm of an intermittent coming upon a sleeping patient; and after constant inquiry for thirty years and more, have not been able to collect a dozen instances in which the state of sleep was not absolutely protective from succeeding paroxysms. Yellow fever, on the other hand, is at least indifferent to it, and not seldom arouses the startled slumberer by its unwelcome visit. Neuralgia seems to respect sleep, no matter how frequent or habitual its annoying inflictions, and rarely, if ever, awakes him with its intolerable pangs, so sure to return within a brief period after his interval of happy forgetfulness is broken.

Some diseases create or engender a tendency to their own recurrence; some give predisposition to other diseases. Of the first we have numerous examples in the paroxysmal and recurrent affections, such as intermittents, epilepsy, asthma, which sometimes leave no trace by which we shall explain their obstinate tenacity. The medical authorities of Great Britain have of late years recognized a form of continued fever, in which this tendency is so characteristic that they have entitled it "relapsing fever." Gout, rheumatism, ophthalmia, leave behind a similar proclivity, perhaps by force of some change in the organic condition of the tissues which they affect.

Instances of the second kind present themselves in the readiness of all other forms of fever to become typhoid in character; in the consecutive dropsies which follow many visceral affections. Smallpox predisposes to pneumonia; measles to diarrhoea; scarlatina to renal disorders. But what shall we say of the opposite or contrasted predisposition, where a disease gives immunity from its own return or protection against the attack of another? Nothing can be more obscure than the question as to the method in which this is brought about. The exanthemata and pertussis, as a well-known rule, affect the constitution but once. This is true of yellow fever; and in a less degree is observed as to typhus and typhoid, and indeed numerous other maladies. Vaccine protects against smallpox still more mysteriously. Those who believe them to be identical, must wonder even more that this protection is not reciprocal; that smallpox, which secures against its own recurrence, does not prevent the vaccine; neither does vaccine interfere with its own second and third intrusion into the organism.

Predisposition is direct and indirect, definite and indefinite. Of the direct and definite we have instances in the latent period of intercurrent diseases and in the stage of incubation. Here the subject is in that doubtful condition formerly alluded to, lying on the boundary between health and sickness; but the tendency is so precise and well defined, however perfectly well he may seem, that we not only know how he is to be assailed, but when. Indirect and indefinite predispo

sitions are found in the relations of sex and age. The maladies of early life are very different from those of advanced age. Croup rarely assails an adult. The exanthemata and pertussis affect childhood chiefly. Male infants are more liable to hydrocephalus than females; girls are oftener subjects of chorea than boys. Women are seldomer assailed than men by bronchitis or apoplexy, and I think also by epilepsy. They are almost exclusively affected with hysteria, and exhibit greatly oftener than the opposite sex the phenomena of chlorosis and anæmia or spanæmia.

II. EXCITING CAUSES OF DISEASE.

Under this general head we speak of all those contingencies which are immediately efficient in deranging the animal economy, and producing an abnormal or morbid impression. They are infinitely numerous and diversified; including indeed all agents which affect the tissues in every way, or vary the composition of the fluids. The air we breathe, the food we eat, the beverages with which we quench our thirst, our dress, our habits, and modes of life and occupations; all the movements and circumstances through and by which we are brought into connection and harmony with universal nature, all may become instruments of destruction and means of death.

Besides these substances and their modes of innocent agency or indifferent character, we are surrounded by a large class of known and unknown influences which impress us only or chiefly for evil, and which are always discordant with the normal and healthful movements of the organism.

The former are injurious only by excess or unadaptedness; the latter by their characteristic qualities or properties; and thus we are led to institute a very obvious but important distinction of the exciting causes of disease into the Incidental and the Specific.

Incidental causes of disease give rise to no uniform or constant modes of derangement; their effect being always relevant to and determined by the existing predisposition, or predisposing condition of the system at the time of their application.

Specific causes may be spoken of as poisons; their mode of disturbance is uniform and constant; their effects, though admitting certain limited modifications, may be definitely predicted; they are independent of, or paramount to, all predisposing conditions of the system. We shall hereafter see that these specific poisons are further divisible into two classes. The first is not absolutely independent of quantity, but admits of a certain extent of safe application which is greatly influenced by habit, and may be distinctly graduated. The second, distinguished by a particular term, is equally and alike efficient-if efficient at all-without respect to amount or quantity applied. Such a cause of disease we speak of as a Virus, and recognize in most of the forms of contagion.

INCIDENTAL CAUSES.

I have attributed the hurtful influences of incidental causes of disease exclusively to excess in amount, or form of application, or to what I have called unadaptedness. I must explain these phrases. Excess is a relative term, whose boundaries are changing and undefinable. It prepares the way for disease and ushers it in by exhausting the vital power of the tissues. If these continue to react, in their own characteristic manner upon impressions made on them unremittingly or in undue vehemence, this exhaustion will be complete and destructive at once. If, on the other hand, they lose the capacity of reaction, and become passive, they suffer, from the presence of any excitant, all such change and disorganization, whether mechanical or chemical, as shall be determined by the nature of such excitant.

Unadaptedness also requires definition and illustration. I cannot find a word more fairly expressive of such occasional condition of any part or parts as shall unfit them to receive an impression not necessarily or in its own nature injurious, but inflicting injury by reason of its discordance with the existing state of the body. Thus, the prehension of food by one laboring under great fatigue will be followed by indigestion. Active exercise of the mind, too, as well as of the muscles, anxious thought or profound study, will also incapacitate the stomach for its functions, and make a simple meal injurious. Hence also habits formed upon diurnal revolutions cannot be traversed with impunity; horses and men that labor by night, instead of by day, wear out prematurely. All habits, however formed, generate a course of movement, any abrupt change of which shall develop this condition of unpreparedness or unadaptedness. The late hours of the city derange the health of the countryman, even though he may devote the same proportion of his time to sleep. Some persons of strong digestive powers are made ill by suppers, because unaccustomed to eat at night.

We may treat of incidental causes of disease under the several divisions of the climatic; the dietetic; the personal; and the social.

1. CLIMATIC.-The word climatic comprises a great diversity of circumstances, atmospheric and geographical; the temperature, moisture, barometric and electrical states, and the prevailing winds of the region or district of country; the soil, surface, and exposures, hill or valley, sea-shore or lake, or river-bank, mountain or plain, forest or prairie.

Heat, although among the most essential of all excitants to the wellbeing of living bodies, is among the most frequent and familiar sources of disease. Its direct effect is shown in its influence upon the circulation, producing apoplexy, phrenitis, hemorrhage. The vital fluid is not exempt from the law of increment of volume upon addition of caloric; and, thus distending the vessels, it occasions congestion, or escapes by transudation, or by disruption, or laceration of tissue at the "part of least resistance." This may differ, in different individuals, at different times, and in different places. Insolation, which, under my own notice, and that of many others, is a cerebral affection-apoplec