Because of their complexity, methods for quantitation of anaphylaxis in large hypersensitive animals ( 1 ) are not readily adapted for the mouse. Consequently, the occurrence of anaphylaxis in mice is customarily determined using death as end point. Attempts have been made to estimate sublethal anaphylaxis in mice by observing the appearance of certain gross signs (ie., cyanosis and convulsions). Because of their subjectivity, these observations are inadequate. Kind ( 2) found that the rectal temperatures of mice surviving anaphylactic shock were markedly decreased.In our laboratory we consistently observed that hemoconcentration occurs in mice undergoing anaphylaxis. We observed signs of anaphylaxis similar to those described by Weiser et al. (3) . Immediately after challenge most of the mice became quiet and huddled in one position. The fur became ruffled and there was mild lacrimation. There soon followed partial paralysis of the limbs and marked cyanosis of the limbs, tail, and snout. Many animals experienced brief but violent convulsions separated by short periods of complete prostration. Nearly all mice which underwent convulsions died within 30 minutes. Nelson et al.(4) reported that the hematocrit of pooled mouse blood was markedly increased following fatal anaphylactic shock. The present study was designed to determine whether or not hematocrit change might be a suitable criterion for determination of anaphylaxis in mice.Methods. Sensitization and challenge. Fol-lowing randomization, female Swiss-Webster mice (22-27 g) were sensitized with 2 IP injections of 0.25 ml of antigen administered 4 days apart. Twelve days after receipt of the initial sensitizing injection the animals were challenged with an injection in the caudal vein of 0.25 ml of antigen. Two antigen preparations were employed: 1 ) alum precipitated bovine serum albumin* with Hemophilus pertussis vaccinet (APBA + HPV), each 0.25 ml containing 1 mg of bovine serum albumin suspended in 2.576 alum (pH 6.5 to 7.5) with lo9 to 1O1O H . pertussis vaccine cells; and, 2 ) the same as above except that H . pertussis vaccine was not included. This antigen preparation is referred to as APBA. A single challenge antigen preparation, bovine serum albumin with H . pertussis vaccine (BSA + HPV) was used. Each 0.25 ml of this preparation contained 4 mg of bovine albumin and 109 to 1010 cells H . pertussis vaccine. Controls included groups of mice sensitized with one or the other of the 2 sensitizing antigen preparations and challenged with saline, mice injected with saline instead of sensitizing antigen preparation and challenged with BSA + HPV, and groups given saline instead of both sensitization and challenge. Hematocrit determination: A modification of the microhematocrit method described by McGovern et al.( 5) was employed. Four-tenths mm I D microprecipitin capillary *Bovine serum albu,min, 3076, sterile, for use as t Pertussis vaccine (whooping cough bacterin), diluent in Rh testing. h o u r Labs. Wyeth Labs.

placing a thermistor at the edge of the mesentery. Direct readings in degrees centigrade are indicated on a control box meter.:Still or cinephotomicrography is accomplished by placing a reflex camera above the field-splitter (Fig. 3 ) . Jmages of both vascular beds are projected onto a ground glass screen from which observations are made and on which the photograph is composed before exposure. Fig. 4 is an example of the type of micrograph obtained.For observations which need not be recorded photographically, the field-splitter is Thermistor recording unit designed and built by M r . John Degelman, Boston Univ. removed and a boom-mounted viewing box is centered above the microscope oculars. Two large, circular fields are thus projected side by side upon an opal glass screen. A mirror mounted above the screen at a 45 degree angle reflects the images so the observer may remain seated while viewing.This method is currently being employed in a comparative study of vascular responses to shock and other stresses.It has been previously shown that a marked hematocrit rise occurs more frequently than mortality during anaphylaxis in mice( 1 ) : hence, in all probability many sub-lethal reactions were recognized. Tt was the purpose of the present investigation to determine if the degree of hemoconcentration in anaphylaxis is a continuous quantitative function of challenge antigen concentration.Methods. Tn this study 2 different sensitizinq-challenge procedures were utilized. Typical signs of anaphylaxis as previously described ( 1 -2) were observed in both procedures. In the first procedure female Swiss-Webster mice weighing 2 2-2 7 g were sensitized with 2 IP injections (given 4 days apart) of 0.25 ml alum precipitated bovine albumin* with Hcrnophilus pertussis vaccine+ (containing 1.0 mg bovine albumin. lo9 to 1O1O pertussis vaccine cells, and 2.5% alum). Eight days after the second sensitizing injection, challenge was effected by a rapid TV injection *Bovine serum albumin, 30% sterile, for use as diluent in Rh testing. Amour Labs.