ADDITIONAL NOTES ON CONTAGION. 243 



by his excretions to the surrounding atmosphere, rendering it thus capable of producing 

 the same disease in those who may be exposed to its influence. 



The communication of this virus from the sick to the well, in whatever form it may be 

 conveyed, as uniformly produces the same disease, as inoculation excites the small pox, 

 or vaccination conveys the vaccine virus. So far, then, there is something in common in 

 the communication of contagious or infectious diseases, which should be accordingly ex- 

 pressed in the language we employ — some of those diseases are conveyed in one form, 

 others in a different ; we should then be equally careful to mark those circumstances in 

 which they differ, as well as those which they possess in common. 



Such an arrangement appears to me not only practicable, but, at the same time, calcu- 

 lated, in some degree, to harmonize the differences of opinion which now separate the con- 

 tagionists and non-contagionists. Under these impressions, I propose to arrange those 

 diseases which are communicable from one to another under three heads. First, those 

 which are communicated exclusively by contact. In this class I enumerate 



The Itch, 



Syphilis, 



The Sibbens of Scotland, 



The Laanda of Africa, 



Frambaesia, or Yaws, 



Elephantiasis, or Leprosy, 



Hydrophobia, and 



The Vaccine virus. 

 Neither of those diseases can be communicated in any other way than by contact; 

 they are, therefore, contagious diseases, in the strict etymological sense of the term. 

 It is also to be remarked, that these diseases are never conveyed through the medium of 

 the atmosphere; actual contact alone can communicate them from one person to another. 

 These diseases, acknowledged by all to be contagious, and so denominated by all wri- 

 ters, have a law of communication peculiar to themselves. But there is a second class of 

 diseases also considered as contagious, which are communicated under different circum- 

 stances, governed, in this respect, by different laws of communication. 



Those to which I now allude are such as are communicated both by contact and by 

 the atmosphere. In this class I arrange 



Small pox, 



Measles, 



Chicken pox, 



Hooping cough, 



