Disease and Its Causes | Page 5

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 amoeb? 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.[1] 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.
In no way is the individuality of living matter more strongly expressed than in the resistance to disease. The variation in the degree of resistance to an unfavorable environment is seen in every tale of shipwreck and exposure. In the most extensive epidemics certain individuals are spared; but here care must be exercised in interpreting the immunity, for there must be differences in the degree of exposure to the cause of the epidemic. It would not do to interpret the immunity to bullets in battle as due to any individual peculiarity, save possibly a tendency in certain individuals to remove the body from the vicinity of the bullets; in battle and in epidemics the factors of chance and of prudence enter. No other living organism is so resistant to changes in environment as is man, and to this resistance he owes his supremacy. By means of his intelligence he can change the environment. He is able to resist the action of cold by means of houses, fire and clothing; without such power of intelligent creation of the immediate environment the climatic area in which man could live would be very narrow. Just as disease can be acquired by an unfavorable environment, man can so adjust his environment to an injury that harmony will result in spite of the injury. The environment which is necessary to compensate for