Definition of Disease : Part 2

Disease and its Causes
by William Thomas Councilman, M.D.

(Page 2 of 16)

The amoeba will move towards certain substances which may be placed in the fluid around it and away from others. In the water in which the amoebæ live there are usually other organisms, particularly bacteria, on which they feed. When such a bacterium comes in contact with an amoeba, it is taken into its body by becoming enclosed in processes which the amoeba sends out. The enclosed organism then lies in a small clear space in the amoeba, surrounded by fluid which has been shown to differ in its chemical reaction from the general fluid of the interior. This clear space, which may form at any point in the body, corresponds to a stomach in a higher animal and the fluid within it to the digestive fluid or gastric juice. After a time the enclosed organism disappears, it has undergone solution and is assimilated; that is, the substances of which its body was composed have been broken up, the molecules rearranged, and a part has been converted into the substance of the amoeba. If minute insoluble substances, such as particles of carmine, are placed in the water, these may also be taken up by the amoeba; but they undergo no change, and after a time they are cast out. Under the microscope only the gross vital phenomena, motion of the mass, motion within the mass, the reception and disintegration of food particles, and the discharge of inert substances can be observed. The varied and active chemical changes which are taking place cannot be observed.

Up to the present it has been assumed that the environment of the amoeba is that to which it has become adapted and which is favorable to its existence. Under these conditions its structure conforms to the type of the species, as do also the phenomena which it exhibits, and it can assimilate food, grow and multiply. If, during the observation, a small crystal of salt be placed in the fluid, changes almost instantly take place. Motion ceases, the amoebæ appear to shrink into smaller compass, and they become more granular and opaque. If they remain a sufficiently long time in this fluid, they do not regain their usual condition when placed again in fresh water. None of the phenomena which characterized the living amoebæ appear: we say they are dead. After a time they begin to disintegrate, and the bacteria contained in the water and on which the amoebæ fed now invade their tissue and assist in the disintegration. By varying the duration of the exposure to the salt water or the amount of salt added, a point can be reached where some, but not all, of the amoebæ are destroyed. Whether few or many survive depends upon the degree of injury produced. Much the same phenomena can be produced by gradually heating the water in which the amoebæ are contained. It is even possible gradually to accustom such small organisms to an environment which would destroy them if suddenly subjected to it, but in the process of adaptation many individuals will have perished.

It is evident from such an experiment that when a living organism is subject to an environment to which it has not become adapted and which is unfavorable, such alterations in its structure may be produced that it is incapable of living even when it is again returned to the conditions natural to it. Such alterations of structure or injuries are called the lesions of disease. We have seen that in certain individuals the injury was sufficient to inhibit for a time only the usual manifestations of life; these returned when the organism was removed from the unfavorable conditions, and with this or preceding it the organisms, if visibly altered, regained the usual form and structure. We may regard this as disease and recovery. In the disease there is both the injury or lesion and the derangement of vital activity dependent upon this. The cause of the disease acted on the organism from without, it was external to it. Whether the injurious external conditions act as in this case by a change in the surrounding osmotic pressure, or by the destruction of ferments within the cell, or by the introduction into the cell of substances which form stable chemical union with certain of its constituents, and thus prevent chemical processes taking place which are necessary for life, the result is the same.

The experiments with the amoebæ show also two of the most striking characteristics of living matter. 1. It is adaptable. Under the influence of unusual conditions, alterations in structure and possibly in substance, may take place, in consequence of which the organisms under such external conditions may still exhibit the usual phenomena. The organism cannot adapt itself to such changes without undergoing change in structure, although there may be no evidence of such changes visible. This alteration of structure does not constitute a disease, provided the harmonious relation of the organism with the environment be not impaired. An individual without a liver should not be regarded as diseased, provided there can be such an internal adjustment that all of the vital phenomena could go on in the usual manner without the aid of this useful and frequently maligned organ. 2. It is individual. In the varying degrees of exposure to unfavorable conditions of a more serious nature some, but not all, of the organisms are destroyed; in the slight exposure, few; in the longer, many. Unfavorable conditions which will destroy all individuals of a species exposed to them must be extremely rare. There is no such individuality in non-living things. In a mass of sugar grains each grain shows just the same characteristics and reacts in exactly the same way as all the other grains of the mass. Individuality, however expressed, is due to structural variation. It is almost impossible to conceive in the enormous complexity of living things that any two individuals, whether they be single cells or whether they be formed of cell masses, can be exactly the same. It is not necessary to assume in such individual differences that there be any variation in the amount and character of the component elements, but the individuality may be due to differences in the atomic or molecular arrangements. There are two forms of tartaric-acid crystals of precisely the same chemical formula, one of which reflects polarized light to the left, and the other to the right. All the left-sided crystals and all the right-sided are, however, precisely the same. The number of possible variations in the chemical structure of a substance so complex as is protoplasm is inconceivable.

New York, Henry Holt And Company.
London, Williams and Norgate, originally published 1913