The present conception of anaphylaxis indicates that symptoms and death occur as the result of the mechanical irritation produced on the cells of the so-called shock organ by the interaction of antigen and antibody. This shock organ has been shown to differ with various animals. Thus, in the guinea-pig, it has been found to be the smooth muscle of the bronchi and bronchioles. A guinea-pig dying in anaphylactic shock presents a definite and characteristic group of symptoms, the most prominent of which is gasping for breath. The animal dies with its lungs in a state of maximal distention. These symptoms are due to a closure of the bronchi and bronchioles, so that while air may be taken into the lungs because the accessory muscles of respiration are brought into play, it cannot be forced out of the lungs. The guinea-pig, therefore, dies in acute asphyxia. In the rabbit, however, the