subset factor?

Hi,

I used subset command, like this:

grupoP = subset(dados, grupos=='P', ?select=c(mortos, vivos, doses,
percevejos, p))

and the variables in select option are numeric.

I tried fit a model with command:

ajuste.logit = glm(cbind(mortos,percevejos)~log10(doses),
family=binomial(logit), data=grupoP)

and the output is:

ajuste.logit = glm(cbind(mortos,percevejos)~log10(doses),
family=binomial(logit), data=grupoP)

Erro em Math.factor(doses) : log10 not meaningful for factors

what is wrong with my commands? Why doses aren't numeric?

Thanks,