dose <- c(.0028,.0056,.0112,.0225,.0450)

dead <- c(35,21,9,6,1)
live <- 40 - dead

cbind(dose,dead,live,dead+live)

estd.p.death <- dead/(dead+live)

plot(dose,estd.p.death,pch=16)
logit <- log(estd.p.death/(1-estd.p.death))
plot(dose,logit,pch=16)
lm.obj <- lm(logit~dose)
a <- lm.obj$coeff[1]
b <- lm.obj$coeff[2]
abline(a=a,b=b)

s<- seq(from=0,to=.05,by=.001)
logit.fit <- a + b*s
prob.fit <- 1/(1+ exp(-logit.fit))

plot(dose,estd.p.death,pch=16)
lines(s,prob.fit)