Incubation

“ And this degree must be one within limits, for while all organisms are plastic and can attune themselves to a greater or less range of variation in their physical environment, there is a given degree at which the processes of life in each species proceed most favourably. It is this particular degree, which differs for different species, which must be attained, if artificial incubation is to be successfully conducted. In other words, the degree of temperature and moisture within the incubation drawer must remain uniform throughout the period of incubation if the best results are to be reached. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ The sudden appearance and displaying of all the Parts after Incubation, makes it probable, that they are not then actually formed out of a fluid, but that the Stamina of them have been formerly there existent, and are now expanded. The first Part of the Chick which is discovered with the naked Eye, is, you know, the Punctum saliens, and that not till three days and nights of Incubation be past; and then, on {144} the fifth day, the Rudiments of the Head and Body do appear. ”

“ Her observations showed that the duties of incubation are shared by both sexes, that the male usually incubates during the night, but “by day the duties of incubation seem to be shared about equally between the two birds, who are close sitters, the eggs seldom being found alone. ”

“ 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. ”

“ 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? ”

“ 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. ”

“ Attention during Incubation.—There is this distinction in the hen: in some, the desire of sitting or incubation is predominant, which they will repeat to the fifth or sixth time in the year, to their emaciation or almost destruction: in others the desire is so slight, that they will probably sit but twice, or even once in the season, and then not steadily. ”

“ Ventilation is provided for and there is an apparatus for controlling the humidity of the air in the incubation chamber. As in Hüppe’s incubator, the bottom is conical in form. The walls of the incubator are of lead-coated steel, and externally they are covered with linoleum; there are two doors, an inner one of glass and an outer one of metal. The temperature may be controlled as in Hüppe’s incubator.
Hearson has designed several forms of bacteriological (biological) incubators, made by Chas. Hearson & Co., Ltd. Some are heated by a petroleum lamp and others by a gas flame. ”

“ 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 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. ”

“ 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. ”

“ The incubation process consists in placing the inoculated plates in a place where bacteria can grow. Leave the plates upside down at room temperature for 48 hours and in a place with no direct light. Then, analyze the colonies present in the agar and compare color, texture, form, etc.
After two days, you can store the plates in a refrigerator (4 a 6oC) for a couple of days.
Activity No3
“Growing microorganisms that live in our body”
Materials:
• Cotton swabs
• 2 Petri dishes
• Permanent marker
Using a swab, take a sample from inside the nose of a classmate. ”

“ Pipette 25 c.c. water sample into flask 6, and 50 c.c. water sample into flask 7.
7. Incubate the two flasks aerobically at 42°C.
8. After twenty-four hours incubation note in each culture:
a. The presence or absence of visible growth.
b. The reaction of the medium as indicated by the colour change, if any, the litmus has undergone.
c. The presence or absence of gas formation, as indicated by a froth on the surface of the medium, and the collection of gas in the inner "gas" tube. [Pg 429]
9. Replace those tubes which show no signs of growth in the incubator. ”

“ 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. ”

“ No sooner has incubation commenced, than the male, full of ardour, evinces the most daring courage, and gallantly drives off every intruder. Perched on a twig not far from his beloved mate, in order to protect and defend her, he seems to direct every thought and action to these objects. His snow-white breast expands with the warmest feelings; the feathers of his head are raised and spread, the bright orange spot laid open to the rays of the sun; he stands firm on his feet, and his vigilant eye glances over the wide field of vision around him. ”

“ Ten minutes later remove the tube containing the suspension, and cool rapidly by immersing its lower end in a stream of running water.
11. Pour three gelatine (or agar) plates containing respectively 0.2, 0.3, and 0.5 c.c. of the suspension, and incubate. [Pg 301]
12. Pipette the remaining 4 c.c. of the suspension into a culture flask containing 250 c.c. of nutrient bouillon, and incubate.
13. Observe these cultivations from day to day. "No growth" must not be recorded as final until after the completion of seven days' incubation. ”

“ Incubate under suitable conditions as to temperature and atmosphere.
8. Animal Inoculation.—
Finally, when dealing with pathogenic organisms, it is often advisable to inoculate some of the impure culture (or even some of the original materies morbi) into an animal specially chosen on account of its susceptibility to the particular pathogenic organism it is desired to inoculate. Indeed, with some of the more sensitive and strictly parasitic bacteria this method of animal inoculation is practically the only method that will yield a satisfactory result. ”

“ I only desire that every patient under inoculation avoid both excesses of heat and cold; that they breathe a cool air; and that their own sensations be the measure of this temperature. Let them act in this respect as if they were in health, and consulted their conveniency alone in the choice of their air. The heat of their body, increased by the disorder, will, it is true, encrease their desire of cool air; and such a degree of cold as would be rather disagreeable in health, will be extremely grateful in the small-pox. ”

“ 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. ”

“ 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. ”

“ The principal vehicle of transmission is man himself. He is also the principal recipient of infection. Germs may be found in the various secretions such as those from the eye, ear, nose, throat, from wounds and in the pus from abscesses; they may be found also in sputum, urine and in the solid excretions. In [Pg 201] these ways they may be transmitted from one individual to another. They may also be carried by animals, insects, food, milk, water, air or any other mode or vehicle. The most common mode of transference, however, is from person to person. ”

“ The doctrine of Liebig, that the vital force manifests itself in two conditions, or rather, that it is known to be in two different states, that of static equilibrium as in the seed, and in a dynamic state, as in that of growth and reproduction, is perfectly applicable to the germs of disease; the static equilibrium is referrible to the matter of vaccine lymph when dried and preserved for use, and the dynamic forces of the matter are known to be in operation during its reproduction and growth in the system of the vaccinated child. ”

“ Johnson as to my benighted condition on the subject of germ-dust, I beg to refer him to the Philadelphia Medical and Surgical Reporter, January 13, 1877, in which I take the ground that the theory of a contagium vivum is the only tenable one by which to account for the genesis and spread of some infectious diseases. The unlimited self-multiplication of definite forms or special phases of force, as, e. g.. in small-pox, scarlatina, etc., is an attribute only of living matter. ”

“ When these new vessels are formed, if they are not reabsorbed into the circulation, they secrete a new fluid called purulent matter; which generally opens itself a passage on the external skin, and produces an ulcer, which either gradually heals, or spreads, and is the cause of hectic fever; or they secrete contagious matter, which has the property of exciting the same kind of inflammation, and of producing the same kind of contagious matter, when inserted by inoculation into the skin of other persons. ”

“ In so delicate a juncture when we are struggling with an oppressive war, what an addition must it prove to the burden, should the small-pox spread fast in the natural way; and what an advantage must it be to render inoculation familiar every-where, and to have a sufficient number of practitioners at hand, who are experienced in the treatment of the disease, and who are well acquainted with the practice and late improvement of inoculation? ”

“ 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 culture of the virus heightens its maleficent properties. This gradual increase of the virulent force is such that, if we take a drop of blood from an animal representing the twenty-fifth term in a series of successive inoculations, and so dilute this drop with water that a drop of the dilution corresponds to one trillionth of the original drop, we get a liquid of which the smallest quantity still displays mortal activity. ”

“ We have now reached a phase of this question when it is of the very last importance that light should once for all be thrown upon the manner in which contagious and infectious diseases take root and spread. To this end the action of various ferments upon the organs and tissues of the living body must be studied; the habitat of each special organism concerned in the production of each specific disease must be determined, and the mode by which its germs are spread abroad as sources of further infection. ”