Skin reaction in Callithrix jacchus penicillata to phytohemagglutinin.

Sixty marmosets (Callithrix jacchus penicillata) were intradermally tested with phytohemagglutinin. It was possible to classify this population into three groups on the basis of the reactions: 1. negatives, 2. those which showed just local hemorrhage, and finally 3. a group which developed a wheal as well as hemorrhage. The biopsy at the site of the reaction demonstrated several microscopic foci. This finding contrasted with the homogeneous cellular infiltration found in the human controls.