Incubation period

“ That is to say, that although, as stated above, the incubation period of yellow fever— the period elapsing between the introduction of the virus into the body and the on-coming of fever— is usually only from three to five days, yet a period of at least twelve days must elapse before that virus, after removal from one human body, can be effectively implanted in another human body. ”

“ In the human subject the period of incubation of the disease is comparatively prolonged, owing to the in susceptibility of the tissues to the action of this poison; there is therefore some chance of obtaining a complete protection or acclimatization of the tissues before the incubation period is completed. ”

“ Quarantine.— Modern systems of land or sea quarantine directed against plague take cognizance of the facts that the incubation period of the disease may extend to ten days, and that plague affects certain of the lower animals as well as man. ”

“ PERIOD OF INCUBATION.—The period of incubation of typhus fever appears to vary considerably in length, but is usually about twelve days. In some cases the interval between exposure to the contagion and the occurrence of the first symptoms of the disease is asserted to have been considerably longer, and in one instance as long as thirty-one days; but it is probable that there has been in most, if not in all, of these cases a second exposure which has been overlooked. ”

“ In man the incubation period is fortunately a very long one, averaging about forty days. Nervous irritability is the first sign; spasms occur in the respiratory and masticatory muscles, and the termination is similar to rabies in the dog. ”

“ After the inoculation of a healthy individual with blood containing the parasite a period varying from four to twenty-one days elapses before the occurrence of a febrile paroxysm. This is the so-called period of incubation, during which, no doubt, the parasite is undergoing multiplication in the blood of the inoculated individual. ”

“ Injections of pure cultures give rise to a similar disease in monkeys and other animals, from whose blood the micrococcus can be recovered, cultivated afresh, and, on injection into other animals, again give rise to the disease. In five recorded instances inoculation— intentional and accidental— of cultures of the micrococcus into man has been followed by the characteristic symptoms of undulant fever after an incubation period of from five to fifteen days. ”

“ If, for example, measles were to break out in a large group of individuals, none of whom had had the disease, the type of curve would be the same. We will produce evidence supporting our theory under another subject. Of course, other factors such as short incubation period and unusual opportunities for spread through mildly ill individuals play a not unimportant role.
CHART I.
The curves of incidence of influenza in Munich, and of deaths in London during the 1889 and subsequent epidemics. ”

“ It is, however, now known that a period of incubation, varying from a few hours to several days, and usually without subjective symptoms, exists. Many instances are recorded in which persons coming into an infected city have remained well for one, two, or three days, but have eventually shared the sufferings of those into whose midst they have come. ”

“ The cervical lymph glands, as well as the lungs, spleen, and liver, may be the seat of secondary nodules.
_In man_, acute glanders is commoner than the chronic variety. Infection always takes place through an abraded surface, and usually on one of the uncovered parts of the body--most commonly the skin of the hands, arms, or face; or on the mucous membrane of the mouth, nose, or eye. The disease has been acquired by accidental inoculation in the course of experimental investigations in the laboratory, and proved fatal. The incubation period is from three to five days. ”

“ The rapid rise to a peak, almost explosive in character, more characteristic of this disease than of any other, is to be explained by the high degree of invasiveness of the organism, by the short period of incubation, by the fact that many of the sick continue at their work, thus spreading the disease, and by the non-immunity of large masses of people, together with the fact that the transmission of a respiratory infection is accomplished much more easily than is any other type of infection. ”

“ Those that died showed all the symptoms of what is called spontaneous splenic fever. The period of incubation lasted as long as eight or ten days, although, in its latter stages, the disease exhibited those startling features which have caused a belief that the incubating period is a very short one—short, that is to say, for those conditions of contagion where the parasite is not deposited in its pure state under the animal's skin. ”

“ Each one of these infinitely minute organisms, if it were received into a human system under favourable circumstances, would rapidly reproduce itself, and after a few days or weeks, corresponding, as already mentioned, to the period of incubation, give rise to a new case of disease—again a new hot-bed for other unprotected persons. ”

“ Syphilitic Periods. (1) period of primary incubation—the time between exposure and the appearance of the chancre, from ten to ninety days, the average time being three weeks; (2) period of primary symptoms—chancre and bubo of adjacent lymph glands; (3) period of secondary incubation—the time between the appearance of the chancre and the advent of secondary symptoms,—about six weeks as a rule; (4) period of secondary symptoms—lasting from one to three years ”

“ In our own epidemic one case occurred in fourteen days after drinking the water, the average time being about twenty days. The general experience at the present time points to an incubation of about three weeks; but it may vary from two to four weeks, or even longer.
It is an interesting question, but one to which I cannot give a satisfactory answer, Why do not all who are exposed to the infecting cause suffer from the disease? ”

“ All persons coming from an infected locality to a post shall be kept under careful observation until the completion of five days from the time of possible infection, either in a special detention camp or in their own quarters; in either case, their temperature should be taken twice a day during this period of observation so that those who develop yellow-fever may be placed under treatment at the very inception of the disease. ”

“ Whence a strong reason against our hazarding inoculation before that age is passed, especially in crowded towns; except where the vicinity of the natural contagion renders it necessary, or the convenience of inoculating a whole family at a time; as it then becomes better to venture the less favourable circumstances of the age of the patient, or the chance of the pain from toothing, than to risk the infection in the natural way. ”

“ In this epidemic the rate of spread can be definitely measured. The maximum occurs later and later as the distance from the center is increased and the percentage of children infected is also easily observed to fall as the time increases. With regard to the 109.5 weeks’ period epidemic the facts are similar though not quite so definite. This seems to show that for at least two strains of organisms the epidemic ceases because the organism has lost its power of infecting. It may be inferred that an epidemic ceases because the organism varies in its potency to cause infection. ”

“ In this way a large contact is made where the skin is sensitive, nearly constant in temperature, but little below blood heat and from which the air is excluded for the time. Long practice permits them thus to judge small differences of temperature expeditiously and with great accuracy; and they maintain different temperatures during different stages of the incubation. ”

“ Scarlet fever, while contagious at all periods, is probably most so during the period of desquamation. The organism may cling to furniture, clothing, etc., and reproduce the disease after very long periods. The contagion may be carried by persons coming in contact with the sick, or the disease may be transmitted through the air of the sick-room or through clothing, utensils, etc., which have been used by the sick. ”

“ Intermittent fever or ague.—— Every typical malarial fever is made up of a series of pyrexial attacks which recur at definite intervals of twenty-four, forty-eight, or seventy-two hours. Each attack consists of a stage of rigor, a stage of heat, and a stage of sweating; these are followed by a period, " the interval," of apyrexia -actual or relative. The duration and intensity of the constituent stages vary considerably. On the whole, they observe a certain proportion to each other; as a rule, the more pronounced the rigor, the higher the fever and the more profuse the sweating. ”

“ The seasons commonly preferred for inoculation, in this country, are the spring and fall. It may be practised with equal safety in the winter, a due regard being had to the temperature of the air in the preparation of the body.
The principal objection to inoculating in the summer months in this climate, arises from the frequency of bilious diseases at that season, to which the preparation necessary for the small-pox probably disposes the body. This caution applies more directly to children, who, at a certain age, are more subject than grown people to a disease in their bowels in warm weather. ”

“ Perhaps one reason why the disease has been supposed to result from exposure is the undoubted fact that it is chiefly prevalent in the winter and spring rather than in the summer. This argument is, however, modified by the fact that the majority of cases do not occur in January or February when the temperature is lowest, but in March, when the opening of spring is in sight. The reason for this is evident when we remember that the cause of the disease is a germ, generally present in the body and needing only a reduced vitality for its successful inroad on the human system. ”

“ This rather complicated technique has been simplified by the later work of Hata, who substituted horse-serum in which the inoculation is made through the upper solidified layer-. The organisms develop anærobically in the lower fluid layers. To succeed in the cultivation of the pathogenic spirochsetes strict anærobiosis is necessary.
Symptoms. The initial fever.— In yaws there is an incubation stage of very variable duration two weeks to six months* [1] — the appearance of the characteristic eruptions being preceded by a certain amount of constitutional disturbance. ”

“ The period of infection is very doubtful. It may be greatly prolonged by complications. This is especially true of small-pox, diphtheria, typhoid and scarlet fevers. The period during which a disease may be infectious cannot be stated definitely. It varies with different diseases, and must be determined according to the symptoms and character of the case. Measles, chicken-pox, and mumps lose the direct power of infection very early, and the infective principle does not remain active for a long period in the room in which the patient has been ill. ”

“ Immediately an animal has been inoculated a period of clinical observation must be entered upon, which should only terminate with the death of the animal. The general observations should at first and if the infection is an acute one, be made daily—later, and if the animal appears to be unaffected or if the infection is chronic, both general and special observations should be carried out at weekly intervals. If the animal appears to be still unaffected, it should be killed with chloroform vapour at the end of two or three months and a complete post-mortem carried out. ”

“ That we may be the more clearly informed of the effect which the first day’s incubation produces upon the egg, we must set out by ascertaining what changes take place in an egg spontaneously, changes that distinguish a stale egg from one that is new-laid, when what is due to the incubation per se will first be clearly apprehended. ”

“ For though epidemic disease requires a special contagium to produce it, surrounding conditions must have a potent influence on its development. Common seeds may be duly sown, but the conditions of temperature and moisture may be such as to restrict, or altogether prevent, the subsequent growth. Looked at, therefore, from the point of view of the germ theory, the exceptional energy which epidemic disease from time to time exhibits, is in harmony with the method of Nature. ”

“ In respect to the choice of matter for inoculation, the principle circumstance to be attended to, is that it ought to be taken from a patient who has the large distinct kind, before the decline of the disease, and that is free from every contagious disorder. ”

“ The periods of tertian fevers, reckoned from the commencement of one cold fit to the commencement of the next cold fit, recur with solar intervals of forty-eight hours, or with lunar ones of about fifty hours. When these of recurrence begin one or two hours earlier than the solar period, it shews, that the torpor or cold fit is produced by less external influence; and therefore that it is more liable to degenerate into a fever with only remissions; so when menstruation recurs sooner than the period of lunation, it shews a tendency of the habit to torpor of inirritability. ”

“ For most purposes the solid media are to be preferred, since bacterial growth appears as a discrete mass and accidental contamination can be readily recognized. Cultures are made by transferring by means of a sterile platinum wire a little of the material containing the bacteria to the medium. The tubes, after being thus inoculated, are kept at suitable temperatures, usually either at 37° C., the temperature of the body, or at about 20° C., a warm summer temperature, until growth appears. For maintaining a constant temperature incubators with regulating apparatus are used. ”