Sentence:  Dogs should be warmly but airily housed; heartily, but not heatingly, fed — old Indian meal, mixed with oatmeal, suppawn, is the best general food, with a small quantity of salt, which is a <WSD>preventive</WSD> against worms ... 
Meaning of the word marked with <WSD> tags:  A thing that prevents, hinders, or acts as an obstacle to.