Page:Popular Science Monthly Volume 37.djvu/831

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contagious diseases, including small-pox, chicken-pox, scarlet fever, typhns fever, relapsing fever; measles, miliary fever, influenza, whooping-cough, and hydrophobia.

In another class, called miasmatic contagions, the germs are propagated in diseased persons, but, as a law of their further development, they must undergo one stage of change outside of the body, in some decomposing organic matter, before they can again produce their peculiar disease in a healthy person, except by inoculation. To these miasmatic contagious diseases belong typhoid fever, yellow fever, cholera, diphtheria, acute consumption, cerebro-spinal meningitis, and erysipelas. When the virus originates entirely in decomposing vegetable matter, we have the malarious diseases: intermittent fever, remittent fever, continued malarial fever, pernicious fever, dengue fever, and chronic malarial infection.

Adopting this classification gives practical advantages without waiting for the demonstration of the particular microbes of each disease or their modus operandi. It is sufficient practically to know that the whole list of infectious diseases is accounted for under well-known laws of microbic generation. Indeed, the pathogenic cause may simply be called a virus; reserving only a distinctive character for each of the classes mentioned, viz.:

1. A virus which reaches full development in the diseased person, ready for infection in another, as in the small-pox class.

2. A virus which must be produced in the diseased person, but is not transmissible to another until after undergoing further development outside of the body; and usually in some decomposing organic matter. This is true of the typhoid-fever class.

3. Where the virus originates invariably in decomposing organic matter, and, after infecting the human subject, is never transmissible directly from one individual to another. This is the malarial class, including all the intermittent fevers, or the agues of slight degree as well as dangerous remittents and pernicious fevers, the intermittent neuralgias, and the "dumb agues."

Numerous other and very extensively prevalent diseases are known to be of microbic origin; among them pneumonia, rheumatism, tetanus, rabies, and the venereal in its numerous forms and phases.

Aside from the advantage of a scientific classification of diseases is that gained in the matter of prevention as well as cure; in both of which much has already been realized.

The means and manner of action of microbes in their destruction of life and health are various, and in some instances, as yet, obscure. As a prerequisite to their infectious development they must gain access to the blood or tissues through the cutaneous exterior or the mucous interior of the body; each species having