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Data are given on the parasitemia and antibody response in pigeons infected with 3 strains of Toxoplasma , of varying virulence. With the virulent RH strain, which killed about 45% of the birds infected with it, a high parasitemia was obtained regardless of the route of inoculation. The time of appearance or persistence of parasitemia was not markedly different in birds infected by different routes. The parasitemia remained high for about 2 weeks or until death; dilutions up to 1:10,000 of the blood of these birds were found infectious for mice. With the less virulent strains lower parasitemias were obtained; there appears to be a correlation between the pathogenicity of the parasite, in any host, and its spread via the blood stream. Parasitemia does not continue after the antibody titer becomes high. Antibody titer in pigeons as measured in the dye test, drops fairly rapidly and antibody may be undetectable less than a year and a half after infection. Persistence of parasites in the brain of infected birds for as long as 33 months has been demonstrated. Toxoplasmas may remain in brain pseudocysts for long periods without stimulating antibody production. The significance of this observation in relation to the value of serological tests in determining the possible toxoplasmic etiology of human chorioretinitis is briefly discussed.

Summary 1. A pyrimethamine-resistant line of Toxoplasma at least 640 times more resistant than the parent strain was developed in vitro. 2. The resistant nature of this line was retained for at least 3 months when the parasite was grown in the absence of pyrimethamine. 3. A pyrimethamine-requiring line of Toxoplasma could not be developed. 4. The drug-resistant nature of this line of Toxoplasma was not demonstrable in vivo.

Five strains of axenized Entamoeba histolytica were established in eggs from chickens of different genetic backgrounds. The eggs of outbred and inbred chickens varied in the proportion of embryos from which the strains of E. histolytica were recovered and there were variations in the numbers of trophozoites recovered from individual positive eggs. It was possible, however, to find individual, single-mated hens which laid only uniformly susceptible or resistant eggs. Susceptibility and resistance to E. histolytica could be demonstrated in embryonated eggs derived both from outbred heterogenous and in highly inbred chickens but eggs from a genetically stable source were relatively constant in the distribution of susceptible and resistant embryos. Except for gross hydrocephalus, tissue reactions were not observed in the chick embryos or in the chorioallantoic, amniotic, or yolk sac membranes. The yolk sac inoculation route and 37 C incubation temperature provided the optimal survival conditions for the amoebae. Infection with avian leukosis virus and interferon production did not seem to play a role in susceptibility and resistance. Neither the presence of E. histolytica cross-reacting, maternal antibody from the hen transmitted transovarially via the yolk sac, or other antiamoebic substances appeared to play a role in the resistance observed in nonsusceptible eggs. Multiple alternating passages of trophozoites in hen's eggs/TPS-1 broth led to an increase in the number of positive embryos and a decrease in embryo deaths.

THE present study was designed to investigate the viral etiology of respiratory illness in infants and young children. One of the technics employed for isolation of the virus was the recently described hemadsorption method of Vogel and Shelokov.1 , 2 With this technic, several strains of Asian influenza A virus were isolated, but the majority of agents recovered were not influenza A, B or C. The noninfluenza agents appear to comprise two newly recognized groups of myxoviruses,3 probably responsible for a segment of common respiratory illnesses in children. Their properties, serologic characterization and the evidence bearing upon their relation to disease will . . .

Hemadsorption, a specific phenomenon dependent on the hemagglutinating property of the virus, was observed in two viruses newly recovered from children with acute respiratory disease. In a study involving 1,738 children in three hospitals, one or the other of the two hemadsorption viruses was recovered from 54 (6%) of 859 patients with respiratory disease. It appeared that the two viruses were capable of causing a wide variety of clinical manifestations, including croup, pneumonia, bronchiolitis, pharyngitis, and mild afebrile disease. Serologic studies suggested that approximately 20% of the respiratory illness severe enough to require hospitalization in the Washington, D. C., area in 1957-1958 was associated with hemadsorption virus infection.

Cell-free transmission of the herpes-type virus of Marek's disease was obtained by demineralized water treatment of infected chick embryo fibroblasts.