THE CAUSE OF INFECTIOUS DISEASE. 2/3 



fectious disease are sometimes in the place 

 where the disease germ enters, sometimes in 

 tissues remote but more disposed toward the 

 disease ; the expression locus minima resis- 

 tentice is used to denote this latter relation. 



From this standpoint we classify those dis- 

 eases as contagious which can be directly com- 

 municated by mere contact with the sick and 

 do not need a go-between ; and as miasmatic 

 or non-contagious those which are not trans- 

 mitted directly from the sick but are caused by 

 external agents. In the great majority of in- 

 fectious diseases both possibilities of communi- 

 cation exist ; one or the other is the more usual 

 merely. In this sense malaria is never natu- 

 rally contagious, but may be artificially com- 

 municated by transfusion of blood ; cholera is 

 generally not contagious ; small-pox is always 

 contagious. The concept contagion is accord- 

 ingly used in a narrower sense than that of 

 infection, and if we depart from this general 

 usage we must always declare the fact and 

 make it abundantly evident. I say this ex- 

 pressly because certain bacteriologists use the 

 term contagion to express the same conception 

 as that implied in the term infection or wound 

 infection. If this is done in the face of usage, 

 of the clinical experience of physicians and of 



the experience of every layman, then naturally 

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