Placental trophoblasts were markedly distended by large numbers of Gram-negative bacteria and stained strongly when exposed to antibodies derived from the serum of infected dogs (Figure 3). Staining was not pres- ent within infected trophoblasts when they were exposed to normal dog serum or when the addition of a primary antibody was omitted. Positive controls were unavailable. Histochemical (Gram and Giemsa)