216 ADDITIONAL NOTES ON CONTAGION. 



We would then be ready to admit, that the yellow fever is a contagious or communi- 

 cable disease, in an impure atmosphere; but not generally so where the air is preserved 

 pure and free from noxious materials. 



This doctrine, too, I believe, will better account for the apparently contradictory facts, 

 which have been urged by the advocates of the two opposing opinions, than any system 

 that has been adopted. 



It will also lead to a system of police regulations, which will best insure us against the 

 ravages of yellow fever when introduced, at the same time it will teach us carefully to 

 guard against the introduction of it from abroad. 



I shall treat this subject more at length upou another occasion, in connexion with the 

 evidences of the importation of the yellow fever into the United States. 



I am, sir, with sentiments of high respect, your's, 

 Dr. Chisholm. DAVID HOSACK. 



NOTE B. (See page 202.) 



Strictures on the classification of Contagious Diseases proposed in the preceding com- 

 munication, contained in a letter from Colin Chisholm, M. D., F. R. S., #c. #c. 



• Clifton, (England,) October 14, 1809. 



Dear Sir, 



You will find in the October number of the Edinburgh Medical and Surgical Journal 

 the observations on contagion you favoured me with some time ago. 



I approve highly of the first part of your paper ; but on reading the third class of your 

 division of contagious diseases, I find myself obliged to dissent, or, at least, to hesitate in 

 affixing entire approbation to it : and, indeed, I have reason to think, that when you have 

 reconsidered the admissions and concessions you have there made, and the tendency 

 which they have to throw all fevers, however arising, except those which are symptomatic 

 of what are called specific contagions, and which comprise the whole of your second class, 

 into an undefined state of anomaly, you may see cause for retracting them, or giving them 

 more limitation. For my own part, I feel more inclined to divide all diseases of conta- 

 gion into two classes, which may be denominated apyrexious and pyrexious ; and as the 

 latter are distinguished, mediately or immediately, by specific causes, they may be 

 'livided into two sections, the symptomatic and the ideopathic. 



