I thought that had been disproven.
The point was made in the symbloism of the remark, pertaining to a VERY fictional, yet allegorical series. Regarding as to whether it happened or not, historians differ in opinion, though until your statement, I have never heard it was even in debate. Which is true, I dunno, but I did find this (Which subsequent references):
http://www.nativeweb.org/pages/legal/amherst/lord_jeff.html
“Smallpox blankets
Despite his fame, Jeffrey Amherst’s name became tarnished by stories of smallpox-infected blankets used as germ warfare against American Indians. These stories are reported, for example, in Carl Waldman’s “Atlas of the North American Indian” [NY: Facts on File, 1985]. Waldman writes, in reference to a siege of Fort Pitt (Pittsburgh) by Chief Pontiac’s forces during the summer of 1763:
... Captain Simeon Ecuyer had bought time by sending smallpox-infected blankets and handkerchiefs to the Indians surrounding the fort — an early example of biological warfare — which started an epidemic among them. Amherst himself had encouraged this tactic in a letter to Ecuyer. [p. 108]
Some people have doubted these stories; other people, believing the stories, nevertheless assert that the infected blankets were not intentionally distributed to the Indians, or that Lord Jeff himself is not to blame for the germ warfare tactic.”
____________________________________________________________
Historian Francis Parkman, in his book The Conspiracy of Pontiac and the Indian War after the Conquest of Canada [Boston: Little, Brown, 1886] refers to a postscript in an earlier letter from Amherst to Bouquet wondering whether smallpox could not be spread among the Indians:
Could it not be contrived to send the Small Pox among those disaffected tribes of Indians? We must on this occasion use every stratagem in our power to reduce them. [Vol. II, p. 39 (6th edition)]