Disease and Its Causes by William Thomas Councilman (early reader books .TXT) 📕

and remove the granules of blood pigment which result. They often join together, forming connected masses, and surround such a foreign body as a hair, or a thread which the surgeon places in a wound to close it. They may destroy living cells, and do this seemingly when certain cells are in too great numbers and superfluous in a part, their action tending to restore the cell equilibrium. The foreign cells do even more than this: they themselves may be devoured by the growing cells of the tissue, seemingly being actuated by the same supreme idea of sacrifice which led Buddha to give himself to the tigress.

The explanation of most of the changes which take place in inflammation is obvious. It is a definite property of all living things that repair takes place after injury, and certain of the changes are only an accentuation of those which take place in the usual life; but others, such as the formation of the exudate, are unusual; not only is the outpouring of fluid greatly increased, but its character is changed. In the normal transudation6 the substances on which the coagulation of the blood depends pass through the vessel wall to a very slight extent, but the exudate may contain the coagulable material in such amounts that it easily clots. The interchange between the fluid outside the vessels and the blood fluid takes place by means of filtration and osmosis. There is a greater pressure in the vessels than in the fluid outside of them, and the fluid filters through the wall as fluid filters through a thin membrane outside of the body. Osmosis takes place when two fluids of different osmotic pressure are separated by animal membrane. Difference in osmotic pressure is due to differences in molecular concentration, the greater the number of molecules the greater is the pressure, and the greater rapidity of flow is from the fluid of less pressure to the fluid of greater pressure. The molecular concentration of tissue and blood fluid is constantly being equalized by the process of osmosis. In the injured tissue the conditions are more favorable for the fluid of the blood to pass from the vessels: by filtration, because owing to the dilatation of the arteries there is increased amount of blood and greater pressure within the vessels, and the filtering membrane is also thinner because the same amount of membrane (here the wall of the vessel) must cover the larger surface produced by the dilatation. It is, moreover, very generally believed that there are minute openings in the walls of the capillaries, and these would become larger in the dilated vessel just as openings in a sheet of rubber become larger when this is stretched. Osmosis towards the tissue is favored because, owing to destructive processes the molecular pressure in the injured area is increased; an injured tissue has been shown to take up fluid more readily outside of the body than a corresponding uninjured tissue. The slowing of the blood stream, in spite of the dilatation of the vessels, is due to the greater friction of the suspended corpuscles on the walls of the vessels. This is due to the loss from the blood of the outstreaming fluid and the relative increase in the number of corpuscles, added to by the unevenness of surface which the attached corpuscles produce.

The wonderful migration of the leucocytes, which seems to show a conscious protective action on their part, takes place under the action of conditions which influence the movement of cells. When an actively moving amoeba is observed it is seen that the motion is not the result of chance, for it is influenced by conditions external to the organism; certain substances are found to attract the amoebae towards them and other substances to repel them. These influences or forces affecting the movements of organisms are known as tropisms, and play a large part in nature; the attraction of various organisms towards a source of light is known as heliotropism, and there are many other instances of such attraction. The leucocytes as free moving cells also come under the influence of such tropisms. When a small capillary tube having one end sealed is partially filled with the bacteria which produce abscess and placed beneath the skin it quickly becomes filled with leucocytes, these being attracted by the bacteria it contains. Dead cells exert a similar attraction for the large phagocytes. Such attraction is called chemotropism and is supposed to be due in the cases mentioned, to the action of chemical substances such as are given off by the bacteria or the dead cells. The direction of motion is due to stimulation of that part of the body of the leucocyte which is towards the source of the stimulus. The presence in the injured part of bacteria or of injured and dead cells exerts an attraction for the leucocytes within the vessels causing their migration. When the centre of the cornea is injured, this tissue having no vessels, all the vascular phenomena take place in the white part of the eye immediately around the cornea, this becoming red and congested. The migration of leucocytes from the vessels takes place chiefly on the side towards the cornea, and the migrated cells make their way along the devious tracts of the communicating lymph spaces to the area of injury. The objection may be raised that it is difficult to think of a chemical substance produced in an injured area no larger than a millimeter, diffusing through the cornea and reaching the vessels outside this in such quantity and concentration as to affect their contents, nor has there been any evidence presented that definite chemical substances are produced in injured tissues; but there is no difficulty in view of the possibilities. It is not necessary to assume that an actual substance so diffuses itself, but the influence exerted may be thought of as a force, possibly some form of molecular motion, which is set in action at the area of injury and extends from this. No actual substance passes along a nerve when it conveys an impulse.

We have left the injured area with an increased amount of fluid and cells within it, with the blood vessels dilated and with both cells and fluid streaming through their walls, and the cells belonging to the area actively repairing damages and multiplying. The process will continue as long as the cause which produces the injury continues to act, and will gradually cease with the discontinuance of this action, and this may be brought about in various ways. A foreign body may be mechanically removed, as when a thorn is plucked out; or bacteria may be destroyed by the leucocytes; or a poison, such as the sting of an insect, may be diluted by the exudate until it be no longer injurious, or it may be neutralized. Even without the removal of the cause the power of adaptation will enable the life of the affected part to go on, less perfectly perhaps, in the new environment. The excess of fluid is removed by the outflow exceeding the inflow, or it may pass to some one of the surfaces of the body, or in other cases an incision favors its escape. The excess of cells is in part removed with the fluid, in part they disappear by undergoing solution and in part they are devoured by other cells. With the diminishing cell activity the blood vessels resume their usual calibre, and when the newly formed vessels become redundant they disappear by undergoing atrophy in the same way as other tissues which have become useless.

When these changes take place rapidly the inflammation is said to be acute, and chronic when they take place slowly. Chronic inflammation is more complex than is the acute, and there is more variation in the single conditions. The chronicity may be due to a number of conditions, as the persistence of a cause, or to incompleteness of repair which renders the part once affected more vulnerable, to such a degree even that the ordinary conditions to which it is subjected become injurious. A chronic inflammation may be little more than an almost continuous series of acute inflammations, with repair continuously less perfect. Chronic imflammations are a prerogative of the old as compared with the young, of the weak rather than the strong.

Chapter V

Infectious Diseases.—The Historical Importance Of Epidemics Of Disease.—The Losses In Battle Contrasted With The Losses In Armies Produced By—Infectious Diseases.—The Development Of Knowledge Of Epidemics.—The Views Of Hippocrates And Aristotle.—Sporadic And Epidemic Diseases.—The Theory Of The Epidemic Constitution.—Theory That The Contagious Material Is Living.—The Discovery Of Bacteria By Loewenhoeck In 1675.—The Relation Of Contagion To The Theory Of Spontaneous Generation.—Needham And Spallanzani.—The Discovery Of The Compound Microscope In 1605.—The Proof That A Living Organism Is The Cause Of A Disease.—Anthrax.—The Discovery Of The Anthrax Bacillus In 1851.—The Cultivation Of The Bacillus By Koch.—The Mode Of Infection.—The Work Of Pasteur On Anthrax.—The Importance Of The Disease.

These are diseases which are caused by living things which enter the tissues of the body and, living at the expense of the body, produce injury. Such diseases play an important part in the life of man; the majority of deaths are caused directly or indirectly by infection. No other diseases have been so much studied, and in no other department of science has knowledge been capable of such direct application in promoting the health, the efficiency and the happiness of man. This knowledge has added years to the average length of life, it has rendered possible such great engineering works as the Panama Canal, and has contributed to the food supply by making habitation possible over large and productive regions of the earth, formerly uninhabitable owing to the prevalence of disease. It is not too much to say that our modern civilization is dependent upon this knowledge. The massing of the people in large cities, the factory life, the much greater social life, which are all prominent features of modern civilization, would be difficult or impossible without control of the infectious diseases. The rapidity of communication and the increased general movement of people, which have developed in equal ratio with the massing, would serve to extend widely every local outbreak of infection. The principles underlying fermentation and putrefaction which have been applied with great economic advantage to the preservation of food were many of them developed in the course of the study of the infectious diseases. Whether the development of the present civilization is for the ultimate advantage of man may perhaps be disputed, but medicine has made it possible.

The infectious diseases appearing in the form of great epidemics have been important factors in determining historical events, for they have led to the defeat of armies, the fall of cities and of nations. War is properly regarded as one of the greatest evils that can afflict a nation, since it destroys men in the bloom of youth, at the age of greatest service, and brings sorrow and care and poverty to many. But the most potent factor in the losses of war is not the deaths in battle but the deaths from disease. If we designate the lives lost in battle, the killed and the wounded who die, as 1, the loss of the German army from disease in 1870-71 was 1.5, that of the Russians in 1877-78 was 2.7, that of the French in Mexico was 2.8, that of the French in the Crimea 3.7, that of the English in Egypt 4.2. The total loss of the German army in 1870-71 from wounds and disease was 43,182 officers and men, and this seems a small number compared with the 129,128 deaths from smallpox in the same period in Prussia alone. In the Spanish American war there were 20,178 cases of typhoid fever with 1,580 deaths. In the South African war there were in the British troops 31,118 cases of typhoid with