There is a certain class of unbelievers who sometimes ask me...

There is a certain class of unbelievers who sometimes ask me such questions as, if I think that I can live on vegetable food alone; and to strike at the root of the matter at once,--for the root is faith,--I am accustomed to answer such, that I can live on board nails. If they cannot understand that, they cannot understand much that I have to say.