In 1958, Toxascaris leonina infection was observed among dogs in Tokyo. The authors obtained this parasite from the intestines of three of six dogs killed for autopsy. Prior to the autopsy these dogs have been kept in a medical school. For a large number of dogs kept there was carried out parasitological examination. Of 112 dogs examined in 1959, 19 (17%) were found infected or egg-positive in the feces, and of 64 examined in 1960, 6 (9.4%) infected. These dogs were mongrels presumed to be more than one year old and weighing 10 to 25 kg. Toxocara canis was observed only in two apparently young dogs, one of which was infected concurrently with T. leonina. In 1960, another canine case of T. leonina infection was observed. It was a Scotch terrier. 4 months old, born and reared in Tokyo. It was also infected with T. canis. The authors think that most of the reports on theoccurrence of T. canis in adult dogs are possibly meager information on T. leonina, and that some researchers referred an ascarid, which is really T. leonina, erroneously as T. canis. The authors have successfully infected dogs by feeding them embryonated eggs involved in natural infection. A larva (of the 2 nd stage) was observed ensheathed at 5 days of incubation. The sheath was kept on for 40 days of incubation. In the case of feeding dogs with embryonated eggs, the prepatent period, or a period from infection to the appearance of eggs in the host feces, was in a range of from 48 to 88 days.
Intranasal inoculation with 15-100 cells of the proliferative form of toxoplasma (Tp) caused no clinical infection in piglets about two months old. In inoculated piglets, no rise in dye-test titer was observed. No positive T.S.C. skin test was given by any one of them. Infection occurred when more than 1, 000 cells of Tp had been inoculated. These results seemed to indicate that the intranasal route was useful for infection. After intraperitoneal inoculation with 200 to 2, 000 cells of Tp, a rise in dye-test titer was observed and a positive T.S.C. skin test was revealed, although no inoculated piglets showed any clinical signs. It was considered that these piglets were suffering from the subclinical infection. Those piglets which had been given more than 20, 000 cells of Tp were infected successfully with clinical symptoms, giving positive dye tests and T. S.C. skin tests. In swine artificially infected, leukocytes increased in number, neutrophils increased in percentage with shift to the left of nuclei, and decreased in number but no change was seen in the number of reticulocytes. These hematological findings were considered to have a very important significance for the differential diagnosis between hog cholera and acute toxoplasmosis of swine.