The Cells of the Deeper Tissues. Cells of the deeper tissues react to slight variations of temperature and changes in osmotic pressure, because such deviations are unnatural to them. The skin should keep the temperature normal, while the intestines and the kidneys should be able to keep the osmotic pressure in the at customary height. These cells possess as well a definite chemical constitution, pro duces a peculiar chemical reaction in the blood, lymph and other fluids of the tissues. Thus, a slight change in the chemical constitution of the blood will produce a. severe aphysiologieal irritation for these cells.
Each organism tries to keep in every way possible a fairly uniform temperature, definite osmotic pressure and chemical constitution for its cells and tissues. When this cannot he maintained, conditions arise which injure the tissue-cells. While the epithelium is acting normally, the body will be healthy. When its functions arc disturbed by outside changes, it becomes sick. This is explained primarily by the direct in fluence of the affection on the skin, and secondarily by the entrance of harmful substances which should normally he arrested by it. etc. For example, when the outside temperature drops below the ordinary endur ance of the skin, the entire body suffers from cold, and death is produced by freezing. The latter conditions are seen when the low temperature injures the mucous membranes, say of the respiratory tract, and makes it sensitive to bacteria, which thus secondarily produce disease (coryza).
From this it is seen how injuries of the epithelium often form the predisposing cause for a disease. They are changes in temperature, trauma, dust and bacteria in the air, and finally a previous faulty nu trition. This latter may arise from too much, too little, or perhaps improper food.
The results of injury to the epithelium are usually seen in the pen etration of foreign substances into the deeper tissues of the body. Here they call forth a reaction, being aphysiological stimuli. These invading substances may be destroyed by this reaction or again appear as a dis ease, more or less severe, when the destruction does not proceed smoothly.
Bacterial Causes of teaches that the sub stances which pass through the epithelium and produce disease in the inner organs are almost exclusively protozoa and bacteria. Now, we know that certain bacteria do not produce disease in man, even when they enter the deeper tissues. Again, there are bacteria which, patho genic to man, do not give a disease when injected into other species of animals. That certain bacteria always produce disease in man but do not show any reaction in other animals is explained by the following: These bacteria meet in the cells of the human species substances which do not exist in the other species, and the consequent reaction produces disease. This peculiarity of reaction is called the Idiosyncrasy of Species.
Since most bacteria produce no disease when they enter the body in small numbers, it is supposed that they die, and that this death is dependent on the reaction produced by the presence of the bacteria in the tissues. In order to produce a disease it is essential for the bacteria entering the body to meet cells which will combat them. These cells in the human species are the leucocytes, either the polyleucocytes or the monoleucocytes. This idea of resistance agrees with the phagocytic power of the leucocyte, discovered by Metschnikoff and Hans Buchner. The leucocytes are the only cells of the body which retain the peculiar ities of the aina'ha, as to migration and digestion. This fact explains certain things we have not been able to fathom. " Why is it that infec tious diseases of the respiratory tract are often accompanied by a high leucocyte count, as in purulent catarrh of the upper air-passages. bron chitis, and pneumonia, while almost none are seen in diseases of the di gestive tract?" The answer to this question is that the cells of the digestive tract are able to protect themselves unaided, while those of the respiratory tract need the leucocyte to help them resist.
The human cell must, by its very nature, react to bacteria by pro ducing disease when they enter the system, in the same way that the muscle-fibre is forced to contract in reacting to an electric stimulus. The amount of the specific cause of a disease (emytagium), be it syphilis or measles, does not matter. The patient will in any event fall sick, even though the quantity lie small.
Not only must mankind react to a certain distinct etiological factor by the appearance of a disease, but this must he a certain definite disease. Men, being similar to one another, must of necessity react to the same stimulus with approximately the same objective and subjective symp toms, thus making it possible for its to diagnosticate a disease. Dif ferent individuals of the same species present a slightly different reaction as a result of the same disease, because of the slight difference of their cells, and in the same Nvily small differences in susceptibility are seen in the same family. We can carry this still further by saying that we may have an individual idiosyncrasy to disease as well as a racial and family one.