This view of infections diseases thus affords the hope and suggestion of a method of diminish ing, if not of getting rid of, such diseases alto. gether, and to some extent also indicates the direction in which their cure is to be sought. If the particular organism of each contagious disease were known, and the conditions of its life and activity understood, there is great prob ability that this knowledge would at once sug gest a method by which its multiplication in the living body could be arrested, and the disease thus cured. The method of treating some in fectious diseases by vaccines (see below), or by antitoxins (p. 513), illustrates this. Even with out such knowledge, however, the view indicates the means for arresting the spread of contagious diseases and diminishing their occurrence. Too often, however, one case is the breeding-ground of a multitude of others, because no steps are taken to prevent the scattering abroad of the germs. To prevent such an occurrence methods are adopted for destroying the disease germs that have proceeded from the patient's body. These methods are stated under DISINFEC TION.
Two misunderstandings must be guarded against. In the early part of this article the grounds were stated for the assertion that the organisms of putrefaction were everywhere, and could not he avoided. There can be no doubt that everyone daily swallows and draws into the lungs hundreds of them. These germs of putre faction are powerless to harm the living human body. Moreover, by no possibility, it would appear, can such organisms be changed into forms capable of acting in a poisonous manner on the living body. To repeat, it is not the ordinary germ of putrefaction that does harm ; it is a particular form of organism for each particular disease. The second point to be noticed is that disease germs may gain entrance to a person's body and yet he may not suffer from the disease. Just as in nature each plant grows best in a par ticular soil, and in sonic kinds of soil certain plants cannot grow at all, so diseas: germs may enter a person's body hut be unable to thrive there. In other words, the person is able to resist the disease. (See Immunity, p. 513.) Just as there are soils that will grow anything, so there are persons who catch everything that is going.
Nothing gives a man so great disease-resisting power as good health. That man secures himself best against infectious as against other disease, who, besides keeping far from the source of the infection, lives regularly and temperately in diet and in conduct.
Vaccines. —Some diseases aro successfully treated by the use of an emulsion of the organ isms, whose operation is the cause of the disease. A pure culture of the organism is made. An emulsion of the pure culture is then produced by rubbing it up with sterile water. The emulsion is then heated to kill the organisms; and an antiseptic is added to preserve the mixture. The strength of the emulsion is then determined by estimating the number of organisms contained in a fixed quantity.
A particular disease is then treated by inject ing, under the skin, a small quantity of such a preparation of organisms to which the disease is due, and this injection is repeated at definite intervals in increasing doses. Such vaccines are employed both to prevent disease, that is to confer immunity, and to cure disease already present.
In treating a disease already present, it is best to find and identify the organism attacking the particular patient, to make the culture of it, to produce a vaccine from this culture, and then to inject this into the patient. This is called an autogenous vaccine, that is a vaccine produced from the very organism attacking the particular person. It is, of course, a somewhat elaborate process, requiring special methods not always ready at hand. There are in the market standard vaccines for the treatment of various ailments in this way, of which the following is a list:— Anti-pneumococcic vaccine, for the treat ment of pneumonia, Anti-streptococcic vaccine, for the treat, ment of suppuration and abscess, Anti-staphylococcic vaccine, for the treat ment of acne, boils, and carbuncles, Anti-typhoid vaccine, for the prevention of typhoid.
Influenza may be treated in this way, and also some forms of bronchial and nasal catarrh, and there are some ailments believed to be due to an organism found in the large bowel — colon bacillus—for which also a vaccine is prepared.
Epidemic and Endemic.—It is the fact of contagion that gives the peculiar character to diseases called Epidemic diseases. One person affected with small-pox conics into a community. In a short time others catch it from him. Each one of these communicates it to others, and thus the disease spreads among the people. It be comes epidemic (Greek, epi, upon, and demos, the people). Small-pox, measles, and scarlet fever are thus types of epidemic diseases, diseases , capable of over-spreading a community in a brief period. On the other hand, such diseases may appear here and there, not spreading for some reason or another, but an odd case occurring un• connected with others, so far as known. Such cases are said to be sporadic. In opposition to epidemic is the word endemic. The essence of an epidemic disease, as we have seen, is a poison, capable of multiplying in a human body, and of being passed from person to person, communicat ing the disease. Now an endemic disease is not one which can be so passed from one person to another regardless of place. It is linked with some particular district, so that a person is not liable to it unless he comes within the affected district, and perhaps by leaving the district he may get rid of it. It depends, that is to say, upon some peculiarity of climate, of water-supply, or drainage of the district in question. Thus goitre (p. 287) affects persons living in certain parts of Derbyshire, in certain Swiss valleys, &c., and persons will not be affected by it if they keep away from the localities where it prevails.