490 Proceedings of Royal Society of Edinburgh. [sess. 
taken as an example. The population numbered at that time 
about 10,000, and about half only were protected by a prior attack 
Diagram V. 
of smallpox; of the remainder, all but 750 persons suffered from 
the disease. Of the latter, a large proportion were probably 
susceptible, though the exact conditions which were necessary to 
Diagram VI. 
cause their infection did not occur. In this case the decline of 
the epidemic was much more rapid than that usually seen,* due 
* Compare Diagram XVII. 
