60 



DR. B. ANGDS SMITH ON ANCIENT AND 



Although there have been intervals of contradiction, the 

 statements have been made early, but perhaps nowhere made 

 so clearly as in a pamphlet written in 1721, entitled — 

 *'u4n hypothetical notion of the Plague, and some out-of-the- 

 way thoughts about it. By Mr. Place." Speaking of infec- 

 tion, he uses the terms — " A body that works another to 

 conformity with itself;" also, "perfect infection — the com- 

 munication of specifical form and motion by matter of superior 

 activity to some of inferior, that is, a substance fitly disposed or 

 naturally capable of being wrought upon." And in few words — 

 "Infection is the communication of motion by activity" — 

 " among particles allied." 



This seems to represent our knowledge of the subject as 

 fully as anything yet said, and indeed more so, although it 

 may not express, like the words of Stahl and Liebig, the 

 mechanical law. If we go so far, we form a theory of the 

 motion ; if we adopt Mr. Place's remarks, we adopt a repre- 

 sentation of the state of our knowledge. 



It may happen that the extreme mechanical mode of stating 

 this law is the right one, although not at present capable of 

 absolute proof; and it may be remarked here that chemistry 

 has gained by the application of mechanical laws in instances 

 where affinity only had been supposed to act. As the most 

 remarkable of all instances may be mentioned the failure of 

 every method of explaining chemical combination, until at 

 once made perfectly clear by what may fairly be called the 

 Mechanical Atomic Theory of Dal ton. 



We may suppose the question of the production of disease, 

 according to the chemical theory, to be put in this form, or to 

 be illustrated by such reasons as the following : — 



1. Permanent chemical compounds, gases or otherwise, are 

 not capable of acting as infections, that is, cannot convey 

 disease directly, although every gas is more or less able 

 to cause death, the atmosphere excepted. Some decompose 

 tha tissues rapidly, and may give rise to other chemical 



