INVISIBLE ASSAILANTS OF HEALTH. 811 



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contagious diseases, including small-pox, chicken-pox, scarlet fe- 

 ver, typhns fever, relapsing fever; measles, miliary fever, influ- 

 enza, whooping-cough, and hydrophobia. 



In another class, called miasmatic contagions, the germs are 

 propagated in diseased persons, but, as a law of their further de- 

 velopment, 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 consump- 

 tion, 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 mala- 

 rial infection. 



Adopting this classification gives practical advantages with- 

 out 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 decompos- 

 ing organic matter. This is true of the typhoid-fever class. 



3. Where the virus originates invariably in decomposing or- 

 ganic 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 perni- 

 cious 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, rheuma- 

 tism, tetanus, rabies, and the venereal in its numerous forms and 

 phases. 



Aside from the advantage of a scientific classification of dis- 

 eases 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 destruc- 

 tion 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 



