1. Histamine does not kill the rabbit by arteriospasm of the pulmonary artery.

  2. The pulmonary arterial bed in rabbits killed with BaCl2 resists high pressures of the perfusion fluid in most of the animals.

  3. Some rabbits are not killed by the lethal dose of BaCl2 for the majority of rabbits.

  4. Rabbits that have received the usual series of sensitizing injections of an antigen and have been found insensitive by test may still die in typical anaphylactoid symptoms upon the injection of BaCl2; therefore the variability in the degree of the anaphylactic reaction in rabbits that have received the same treatment with egg white and horse serum is not due to a corresponding variation in the general reactivity of the pulmonary medial muscle to stimulation.

  5. Histamine, epinephrine and BaCl2 may produce a characteristically different effect (contraction, relaxation of normal tone, no change) upon the same unstriated muscular tissue (bronchial) in the same animal.

  6. Unstriped muscle from different sites in the same animal may be affected in quite different manner by the same substance.

  7. The same substance usually produces the same qualitative effect upon the unstriped muscle of the same organ in guinea pig and rabbit.

  8. The action of a substance upon the isolated unstriped muscular tissue in the bath is not always reflected in the physiologic action of the substance upon the same tissue in the living animal.

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