IT is a well known fact that leukopenia and thrombopenia regularly accompany anaphylactic shock in every species of animals.1 In 1924 Webb2 made an extensive study of the leukopenia which occurs in sensitized dogs as a consequence of the injection of the antigen. Recently, Kopeloff and associates3 and Kinsell and co-workers4 have shown that a decrease in platelets is definitely proportionate to the gravity of the anaphylactic shock in monkeys and rabbits. They have also postulated that a rupture of those hematologic elements might help to explain the liberation of histamine, since rabbit platelets are especially rich in histamine.5 In the case of dogs, however, it is not so easy to explain the increase of histamine in the blood as a consequence of an explosion of platelets, since those elements are very poor carriers of histamine in this species of animal. Moreover, it has been