ADDITIONAL NOTES ON CONTAGION. 247 



If a febrile disease has for its cause, an aura, a gaseous fluid, emanating from the body 

 of a man labouring under that fever, which will manifest activity only within a certain, 

 generally definable, distance from that body, how can we with any propriety of concep- 

 tion or language, say, that such a disease is only communicable through the medium of an 

 impure atmosphere ? Again, is not a fever proceeding from the action of marsh mias- 

 mata different from the fever we have just been considering, inasmuch as the one is not 

 communicable — the other is certainly communicable from the subject of it to be a healthy 

 subject ? How then can we admit such a proposition as the following : " In an impure 

 air, rendered so by the decomposition of animal and vegetable substances, as takes place 

 in marshy countries, or by concentrated human effluvia, as in camps, jails, hospitals, or on 

 shipboard, they (your third class) are rendered, not only extremely malignant and mor- 

 tal in themselves, but become communicable to others who approach the sick, or breathe 

 the same atmosphere which has become assimilated to the poison introduced, insomuch, that 

 the same specific disease is communicated, whether it be plague, yellow fever, typhus, or 

 dysentery ? Pardon me when I say I do not understand this ; when I say I perceive a 

 marked inconsistency in it ; several causes of an opposite nature producing effects all 

 partaking of one general principle, contagion. Is not this a very near approach to the 

 heterogeneity I have apprehended ? I suspect that dysentery does not come with marked 

 propriety into the same class with plague, yellow fever, (malignant pestilential,) and ty- 

 phus, for it is certainly oftener the product of marshes than morbid animal effluvia, and 

 partakes very often of the type of intermittents. When I thus object to your classifi- 

 cation as it relates to pyrexious contagions, I fully admit the occurrence of hybrid fevers, 

 that is, contagious fevers with the types of those we know to proceed from the action of 

 marsh miasmata. But on these occasions, all the conditions which constitute pyrexious 

 contagions are present ; their form is only a little changed ; their nature is unaltered : 

 they are communicable only within the radius of contagion. That plague, or yellow fever 

 (by which I understand the fever to which I have given the name malignant pestilential,) 

 more especially, "are only communicable through the medium of an impure atmosphere ;" 

 that in a pure air, in large and well ventilated apartments, &c. they are not communicat- 

 ed, or very rarely, are propositions which I much doubt, because they are most certainly 

 in direct contradiction to my own experience. I speak more immediately concerning the 

 malignant pestilential fever. Were this a fact sanctioned by universal experience, (for- 

 give the pointed expression, it is only for your own eye,) the extirpation of this fever 

 might, in general, be a very easy operation. But I have seen too many proofs of its con- 

 tagion communicating itself to healthy persons in a pure atmosphere, to admit the vali- 

 dity of your definition of it. If healthy persons, or persons possessing every internal 



