Vaccination of mice with CPV/49. Mice were inoculated i.p. with 5 × 105 TCID50 of CPV/49 (c and d) or unsupplemented medium (a and b). Mice were challenged 28 days later with 5 × 105 TCID50 of CVB3/M. Ten days after challenge, mice were sacrificed, and hearts (a and c) and pancreata (b and d) were fixed in formalin, sectioned, and stained with hemotoxylin and eosin. Mice inoculated with CPV/49 and challenged 10 days later with either CVB3/M or CVB3/AS produced results similar to those shown here (data not shown). Original magnification, ×100.