But for some reason, textbook summaries tend to leave out some of the more specific details -- for instance, Pavlov never actually used bells, but rather relied on metronomes and electric shocks to condition his dogs. Oh, and he measured the dogs' saliva by removing their esophagus and cutting holes into their goddamned necks so that food would just fall out, no matter how much they ate.
See, Pavlov was interested in measuring conditional and unconditional responses, meaning responses that were triggered by specific associations (the metronomes and electric shocks) and responses that were triggered by the act of eating itself. By cutting little food trapdoors into each dog's throat, he was able to measure how much saliva was being produced by the act of eating. But don't worry -- Pavlov didn't stop there. He carved many holes into each of his test pooches, tracing along their digestive tracts to measure how much gastric fluid was being generated by the act of eating (remember, the dogs weren't actually consuming any food -- it was falling out of their neckholes as fast as they could swallow it).
Unsurprisingly, in addition to proving a connection between association and physical response, he also succeeded in killing a shitload of dogs. He lamented the loss of a particular dog after draining it of stomach juices for 10 straight days as follows: "Our passionate desire to extend experimental trials on such a rare animal was foiled by its death as a result of extended starvation and a series of wounds."