The acute inflammatory reaction has been extensively studied and several of its parameters quantitated. The most thorough measurements involved changes in blood flow, vascular permeability, and leukocyte infiltration. Although hemorrhage has often been observed in inflammatory reactions, to our knowledge, no satisfactory technique has been developed which is sensitive enough to quantitate it in cutaneous lesions. However, hemorrhage into soft tissues can be quantitated as shown by Schertzer and Ward ( 1 ) by homogenizing the tissue, and, following extraction, estimating the h e m o g l o b i n c o n c e n t r a t i o n s p e ctrophotometrically . A similar approach was attempted in our laboratory. Hemoglobin was extracted from hemorrhagic skin lesions by the method of Dodge et al.(2), but this method proved to be too insensitive in our system. A second approach was to use "Cr or '"In to label red blood cells (RBCs) in vitro followed by their reinfusion. These techniques proved feasible, but sensitivity of the assay was greatly improved when RBCs were labeled in virw with .' "e. In initial experiments the RBCs were labeled in the rabbits in which dermal lesions were induced. Subsequently the RBCs of a donor rabbit were labeled in vivo and then transfused into recipient rabbits. Hemorrhagic lesions were induced in the skin of recipient
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