The skin of the rabbit's ear is considerably more resistant than the abdominal skin to the phenomenon of local skin reactivity to bacterial filtrates. Ten times the provocative dose is required if it is given into the vein of the prepared ear and thirty times the provocative dose if it is given into the vein of the non-prepared ear.
The state of reactivity cannot be elicited by a preparatory intravenous injection of bacterial filtrates alone into clamped and non-clamped ears. The state also fails to appear in combination with cold, xylol, ethyl urethane, pilocarpine hydrochloride, atropine, calcium gluconate, guinea pig liver extract, histamine dihydrochloride, adrenalin chloride, and pituitrin.
Preparatory intravenous injections of toxins are capable of eliciting the state of reactivity in the rabbit's ear when they are accompanied by thermal hyperemia (i.e., exposure to 45°, 50°, and 55°C.). It is also possible to induce the state of reactivity when a mixture of the preparatory factors with testicular extract is given into the veins of clamped ears. The incubation period required may be less than 2 hours.
In the light of the above experiments, there are discussed various observations concerning the elicitation of the phenomena of organ reactivity by means of live bacterial cultures and the filtrates thereof.