1. Platelet counts have been made in dogs which showed typical anaphylactic shock judged by the blood pressure tracing.

  2. Within two to ten minutes after the injection of the antigen in sensitive animals the platelet count reached a level of from 2½ to 20 per cent of the count before injection.

  3. The majority of these counts in shock were less than 50,000/mm3 and all showed clumping of the platelets to the extent of from 40 to 90 per cent.

  4. Injection of heparin before the antigen did not prevent the low count or the clumping.

  5. The low platelet counts also occurred when anaphylactic shock was obtained in the anaesthetized liverless animal.

  6. The decreased coagulability of the blood in the liverless dog in anaphylactic shock appears to be due to the lack of platelets in the circulating blood.

  7. In canine anaphylaxis the platelet count is of value in indicating sensitivity in mild or doubtful cases.

  8. Peptone in a dose of 0.3 g/kilo produced a reaction in dogs very similar to anaphylactic shock in its effect not only on blood pressure but also on the platelets.

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