NATUBE OF MIASM AND CONTAGION. 45 



common bacteria of putrescent matters, while micrococci, 

 according to Cohn, Klebs and Hirschfield, are not to be con- 

 sidered as the ferment of putrefaction. (American Journal, 

 page 542, Oct. 1873.) 



This is the first recognition of a particular form of micro- 

 organism in connection with a given condition that has stood 

 against adverse criticism. 



EVIDENCE UNSATISFACTORY. 



Within a few years a great mass of such evidence as this 

 was accumulated. It will be seen at once that this kind of 

 evidence is fractional and not conclusive. It shows the 

 presence of rnicro-organisms, but it is in no way conclusive as 

 to the practical effects of these organisms in causing any given 

 disease. It was not shown that the disease could not progress 

 without the organisms. 



NATURE OF MIASM AND CONTAGION. 



During this time a theory was developed for the explana- 

 tion of the spread of certain epidemic diseases, which deserves 

 mention, not only for its intrinsic merit, but for the reason 

 that it has, by directing thought into new channels, greatly 

 enlarged our knowledge of the cause of epidemics and 

 increased our means of defence against them. We have here- 

 tofore spoken only of miasras and contagions. 



A miasm, according to the germ theory of disease, is an 

 organism developed, under certain circumstances, in the soil, 

 decaying vegetation, marshes, etc., of certain localities, which 

 can enter the human body and cause disease, but cannot grow 

 a second time in the body of another person at least does not 

 pass from the sick to the well and is, therefore, not a con- 

 tagion. 



A contagion is an organism whose habitat, by nature or 



