DISEASE, GERM THEORY OF, the theory that certain enthetic diseases have their origin in vegetable germs that have found their way into the body and there undergo processes of growth which lead to chemical changes. The theory has been held with more or less dis tinctness for at least three centuries. To animalcules and micro-organisms were attributed diseases such as pleurisy, epilepsy, smallpox, the measles, syphilis, and malaria. The researches up to this time were, in 1762, summed up by Plenciz, a doctor of medicine in Vienna, who traced infectious maladies back to micro organisms in the form of animate vege table and animal forms. Decomposition was shown by him to be the result a the development of living organisms, which, it was suggested, had been transmitted through the air. Before Plenciz had made the results of his researches public, Needham had promulgated his theory of spontaneous generation, following which a line of physicians, as a result of investi gation with instruments of ever-increas ing accuracy, established the principle that life could only be engendered by previous life and that the germ theory alone was capable of explaining the general phenomena of certain diseases. These investigations disclosed that all germs were not harmful, and that they infected the air in infinite variety, en tering the body through every available channel, the mouth, nose, throat, and gastrointestinal canal. However, the body is provided with a strong defense against its numberless enemies in its covering of skin, the mucous membrane, the lym phatic glands, the phagocytes of certain cells, and the antitoxins in the fluids of the blood.
Observation of the action of certain germs shows that in diphtheria parts of the mucous membrane of the throat are destroyed, while in typhoid fever the in testinal ulcers are caused by the action of the typhoid bacillus. Other groups
of bacteria result in the production of certain poisons which are distributed through the body by the circulation of the blood resulting in prostration and fever. While in regard to certain mal adies the germ theory of their origin still remains only a theory, scientific knowl edge of the relation has been established in respect to an ever-enlarging group, in cluding such diseases as erysipelas, gonor rhoea, diphtheria, influenza, anthrax, actinomycosis, cholera, typhoid, tuber culosis, infantile spinal paralysis, tetanus, leprosy, malaria, pneumonia, syphilis, and relapsing fever.
Culture, cover-glass preparation and animal inoculation are the methods em ployed in modern bacterial examination, coagulated blood serum, Litmus milk, glucose agar-agar, potato agar-agar, and glucose gelatin are employed as culture media. In the technique employed in cover-glass preparation the pathological material is obtained during life and streaked over cover-glass, and after certain processes of heating to fix it, is placed under the microscope and exam ined. In animal inoculations the ma terial is inserted or injected under the skin of a mouse or guinea pig, the progress of the malady is watched; and after death autopses of the organs are made. The presence of tuberculosis is ascertained by examination of the sputum by cover-glass preparation, and by parallel methods the bacillus of diph theria, the plasmodium of malaria, and the germs of other diseases are indicated.