It has been possible to sensitize guinea pigs by the intratracheal administration of small amounts of horse or cow serum. The degree of sensitiveness is comparable to that obtained when the same doses of serum are injected into the peritoneal cavity. Nevertheless, relatively small amounts of foreign protein are slowly absorbed through the lining membranes of the lower respiratory tract. In sensitive animals it has not been possible to produce shock by intratracheal injection of amounts of serum which injected into the peritoneal cavity of other animals of the same series sensitized in the same manner always produced shock. Considerably larger doses administered intratracheally may give rise to anaphylactic symptoms. It is possible that the force necessary to inject the larger amounts of serum may have led to injury and more rapid absorption.

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