Adaptation (a3136)

ADAPTATION (from Latin adaptare—to adjust), the adjustment of living beings to surrounding conditions. Adaptation is a passive process and reduces to the reaction of an organism to changes in physical or physicochemical environmental conditions. Examples of adaptation: In freshwater protozoa, the osmotic concentration of the protoplasm is higher than the concentration of the surrounding water. During the absorption of water, constant desalination occurs within it. The osmotic equilibrium, which is disturbed in this process, is regulated by the activity of the contractile vacuole, which removes excess water from the body. Some protozoa are capable, however, of adapting to existence in more saline and even seawater. In this case, the activity of the contractile vacuole in them slows down and may even cease entirely, since in these conditions, the removal of water from the organism would lead to an increase in the relative concentration of ions in the protoplasm and, in connection with this, to a disturbance of the osmotic equilibrium within it. Thus, in this case, the mechanism of adaptation reduces to a direct physicochemical reaction of the protoplasm.

In other cases, the mechanism of adaptation appears more complex and cannot always be immediately broken down into elementary factors. Such are, for example, the adaptation of animals to temperature conditions (the lengthening of the fur of mammals under the influence of cold), to phenomena of radiant energy (phototropism of plants); the change in skin coloration of cold-blooded animals, thanks to the reaction of pigment cells; the seasonal dimorphism of the coloration of birds and mammals; the change in their coloration depending on climatic-geographical conditions, etc. However, even here, the mechanism of adaptation can, in the final analysis, be reduced to the physicochemical reactions of the protoplasm. The phenomena of adaptation are closely connected with the evolution of organisms and represent one of the most essential factors of acclimatization (see), the struggle for existence, and mimicry (see). Among the least resolved questions connected with adaptation belongs the question of the inheritance of properties arising in the process of adaptation (see Adjustment, Evolutionary doctrines).

G. Epstein. Ocular adaptation, the adjustment of the retina to various degrees of light stimulation. Experience shows that upon moving from a light space into a dark one, our retina must gradually accustom itself to weak illumination so that the eye becomes capable of seeing the surroundings, since the retina, accustomed to strong light stimuli, is in such a state of reduced excitability that a weak light stimulus can no longer evoke distinct visual sensations; this ability of the eye to distinguish surroundings with ever-increasing clarity grows only gradually. Likewise, upon moving from a dark space into a brightly lit one, our eye initially experiences a state of blinding and only then adapts to the bright illumination. The first state is called dark adaptation, the second—light adaptation. The adaptation of the retina occurs according to known laws, the deviation from which serves as a sign of an abnormal state of the organ of vision. Dark adaptation increases approximately 2 to 2.5 times every 2 minutes, and in 40–45 minutes the retina reaches the maximum of its sensitivity, i.e., the moment when it is capable of distinguishing the smallest amount of light characteristic of it (threshold of stimulation). Light adaptation occurs more rapidly.

v. Cherkovskiy. Adaptation of microbes, accommodation of microbes, adaptation of microbes to the environment. Their structure, physiological properties, and chemical composition depend both on the hereditary properties of the given species and on the influences of the environment. The latter force the microorganism to change. These changes were recently considered random and, according to the doctrine of Conn, of little significance for the basic traits of the microorganism, which were considered immutable. However, over time, first timidly and then more decisively, the doctrine of the variability of microbes as a biological factor was put forward, and at present changes in microbes are no longer considered only random, but are also recognized as more profound. The nature of microbial variability depends on two factors: the individual species stability of the given microbe and the depth, scope, and strength of the influence of the environment. Some species of microbes, such as the acid-resistant group, diphtheria forms, and fungal forms, change less and adapt poorly, whereas the typhoid, capsular, coccus, and anaerobic groups are more susceptible to change. The adaptability of microbes is primarily manifested in their relationship to oxygen and ambient temperature. It is known that anaerobes can be accustomed to free oxygen, and vice versa. The same can be said about their relationship to ambient temperature, as well as to the reaction of the medium, to the action of light, and to the chemical composition of the nutrient material. One condition must be observed to reveal this adaptation: the gradual action of new factors. The slower and more gradual the action of new conditions, the more easily and perfectly the microorganism adapts. This adaptation proceeds in various directions. Environmental conditions force the microbe to become less demanding in its physiological functions, to limit them to a minimum, and to pass into a state of anabiosis ('hidden microbism'), for which it forms spores and is surrounded by impermeable mucous, calcareous, and connective tissue capsules (cocci, tubercle bacilli, etc.); or else microorganisms undergo morphological changes, losing entire organs and parts particularly sensitive to ordinary conditions [for example, trypanosomes, when accustomed to arsenic, lose blepharoplasts (Verbickiy)], and thus new races of microbes are obtained. The formation of new races with new properties occurs especially easily when the microbe encounters new chemical substances in the body in which it is accustomed to multiply freely. When harmful substances appear in such an environment, part of the microorganisms perish, while the most resistant individuals survive and give rise to the so-called 'resistant' or 'stubborn' races (Ehrlich). Such resistance has been proven in relation to various chemical compounds and alkaloids (arsenic, alcohol, quinine).- The adaptability of microbes can also proceed in the opposite direction - toward an increase in their viability and acquisition of greater activity. Thus, a little virulent microbe, under the influence of a weakened organism, begins to multiply rapidly and produce toxins, which it did not have before or had in small amounts. An example here can be the numerous cases of so-called endogenous infections, when pneumococcus under the influence of a cold causes pneumonia or Bact. coli under the influence of dietary errors causes a dysentery-like disease. This 'activation' of the microbe is nothing other than its adaptation to new conditions. The phenomena of adaptation are particularly well studied and numerous where the microbe encounters an immune organism or immune media. In addition to the capsules mentioned above, which serve the microbe as a protective layer from the external environment, the microbe begins to produce aggressins (see), which make it less accessible to phagocytes. The adaptability of microbes goes so far that they can become resistant even to immune sera. Bordet as early as 1895 showed how the cholera vibrio can be accustomed to a bacteriolytic serum. A number of authors have proven the possibility of teaching agglutinating microbes to stop agglutinating. And conversely, non-agglutinable microbes can be turned into agglutinating ones, for example, by passing through the bodies of animals and even by simple transfers from one medium to another. The experiments of Levaditi and Roche on changes in the resistance of spirochetes in the body of a rat infected with spirochetes are extremely demonstrative. In these experiments, it turned out that the spirochetes of the first and second attacks differ from each other in their resistance to the bactericidal action of serum: the spirochetes of the second attack are much more virulent than those of the first.- The influence of the animal organism on microbes and the changes in the latter represent such a widespread phenomenon that it has already proven expedient to take them into account in practice, for example, in the immunization of humans and animals. Thus, to obtain an active serum against human streptococcus, the latter should not be passaged through animals. Furthermore, autovaccination usually gives a better effect than heterovaccination. However, this does not exhaust the ability of microbes to accommodation. By restructuring their morphological and physiological traits, the microbe, depending on the soil in which it lives and depending on other microbes multiplying alongside it, can acquire traits characteristic of its neighbor and turn into a so-called 'paramicrobe'. Such a microorganism, as Rosenow proved, can acquire new properties obtained from its cohabitation with a pathogenic microbe and retain them for a long time by inheritance. Thus, for example, a streptococcus isolated from meningitis caused by the diplococcus Weichselbaum's acquires the ability to cause meningitis. A kind of imitation of another pathogen is obtained. This imitation is expressed either in the ability to cause the same disease or in the acquisition of new antigenic properties. Thus, the proteus living in the body of a typhoid patient begins to agglutinate with the patient's serum, although it is not the causative agent of the disease. From all the facts presented, it is clear how important the phenomena of microbial adaptation are for pathology and epidemiology.

S. Zlatogorov. Psychic adaptation, the tendency of certain sensations and feelings to gradually weaken under prolonged continuous action of the same irritation to a level at which they are actually indistinguishable to consciousness; thus, visual sensations tend to be reduced to a neutral gray color, smell and taste become imperceptible, the feeling of pleasure weakens to indifference, etc.