during world war i$,$ a particularly lethal form of the flu killed about $40$ million people around the world. The epidemic started in an army camp of $45,000$ soilders outside of Boston, where the first soldier fell sick on sept $7,1918.$ with time, t$,$ in days since sept $7,$ values of of the constants in the SIR model, dS$/$dt $=-$aSI dI$/$dt $=$ aSI$-$bI$,$ are estimated to be a$=0\mathrm{.}000267$ and b$=9\mathrm{.}865$