Investigations of some aspects of dermatology have been hampered by the lack of an animal whose skin reacts to various irritants with the production of bullae. The guinea pig, which has been employed frequently for studies of eczema, will occasionally acquire subcorneal, intraepidermal (commonest) and subepidermal (rarest) vesicles. These are predominantly microscopic in size and arranged in long fissures, the latter apparently being due to the structure of the skin of the guinea pig. That these vesicles cannot be produced regularly is indicated by Bloch's studies with "primin," an antigen extracted with ether from the fresh leaves of the primrose (Primula obconica).1Furthermore, because of their size and shape and the rapidity with which they dry, the contents of vesicles on the skin of the guinea pig are not readily available for analysis. Goldblatt2described an infectious, polymorphous eruption in guinea pigs which had as its most characteristic