244 ADDITIONAL NOTES ON CONTAGION. 



Scarlet fever, and 



Cynanche maligna. 

 Contact, or the close approach to the sick, labouring under these diseases, will commu- 

 nicate them to those who are susceptible of their influence — but they are no less commu- 

 nicable through the medium of the atmosphere. A second law, which governs the commu- 

 nication of this class of contagious diseases, is, that they are communicable in every season, 

 in the heat of summer, as well as in the cold of winter— in a pure as well as in an impure 

 air, though more readily by the latter than the former. A third law of communica- 

 tion in this class of diseases is, that the persons afflicted with them are not generally 

 susceptible of a second attack. I say generally, because exceptions are related upon 

 very respectable authority. 



This second class of contagious diseases is, therefore, abundantly distinguished from 

 the first ; but they are still associated by most medical writers under the same head of 

 contagious diseases, without assigning to each class its discriminating characters. 



The same want of discrimination has, in my opinion, occasioned the numerous disputes 

 ■among physicians relative to the contagiousness and non-contagiousness of those fevers 

 wftich I enumerate as the third class of diseases that are communicable from one person 

 to another. Under this head I arrange 



Plague, 



Yellow fever, 



Typhus, jail, ship, hospital, or lake fever, and 



Dysentery. 

 These diseases are only, in general, communicable through the medium of an impure 

 atmosphere : in a pure air, in large and well ventilated apartments, when the dress of the 

 patient is frequently changed, all excrementitious discharges immediately removed, and 

 attention paid to cleanliness in general, these diseases are not communicated, or very 

 rarely so, from one to another. But in an impure air, rendered so by the decomposition 

 of animal and vegetable substances, as takes place in low marshy countries, or by concen- 

 trated human effluvia, as in camps, jails, hospitals, or on shipboard, they are rendered not 

 only extremely malignant and mortal 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 the plague, yellow fever, typhus, or dysentery. 



Hence we account for the fact stated by Sydenham, and other writers on epidemics, 

 that the prevailing disease swallows up all other disorders ; i. e. that during the prevalence 

 of an epidemic plague, typhus, dysentery, or other diseases of this class, every indisposi- 





