Studies were made on some biological properties of strains of influenza virus virulent and avirulent for mice.
Four avirulent strains had a rather weak multiplying capacity and their titer in mouse lung was only 10^3.5-10⁵ EID₅₀/0.1ml. Four virulent strains had a strong multiplying capacity and their titer reached 10⁶-10^7.75 EID₅₀/0.1ml. The duration of virus titer was longer in the virulent strains than in the avirulent ones.
Contact infection was not observed in 3 avirulent strains. It was observed in only half of 6 contact mice when two of the 4 virulent strains had been used.
There was no relationship between the pathogenicity of the virus for mice and its hemagglutinating activity to erythrocytes from man, mouse, giunea pig, and chick.

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Twenty-one temperature-sensitive (ts) mutants were isolated from group II RNA phage GA after nitrous acid mutagenesis. They formed plaques at 32°C, but not at 40°C. The eclipse period, latent period, and burst size of GA were 18 minutes, 25 minutes, and 800 at 37°C, respectively.
Cell cultures infected with moi of 5 of these ts mutants were incubated for 40 minutes, first at 40°C and then at 32°C. Release of progenies began 1 minute after the temperature-shift for ts, 20, but was delayed by 14 to 28 minutes for ts 4 and ts 25. From the results of temperature-shift experiments, the 21 ts mutants were classified into 3 groups; that is, early (E), middle (M), and late (L) function mutants. The E mutants (6 ts mutants with ts 25) were thought to have been blocked in the early stage of infection. The M mutants (5 ts mutants with ts 4) and L mutants (10 ts mutants with ts 20) were presumed to have been middle and late function mutants, respectively.
The ts mutants were examined for ability to produce serum-blocking power (SBP) at a nonpermissive temperature (41°C). The L mutants produced much SBP (about 50% of GA) at 41°C, but the E mutants produced no detectable amounts of SBP. The SBP of the M mutants was less than 11 phage particles per induced cell.
The grouping of the ts mutants based on physiological properties was in good accordance with the results of the complementation test. These results suggest that the E mutant may probably be a replicate one and the M mutant a coat protein one, and that the L mutant may have a defect in the A protein cistron. Asymmetric complementation was observed for the first time in group II RNA phage GA. In the cross between ts 4 (M mutant) and ts 11 (L mutant), about 79% of the total progenies produced were ts 4.

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The development of Mumps fluorescent and neutralizing antibody in saliva and its relationship to virus excretion were studied in the case of natural infection. The antibody produced in serum was also measured in comparison with that in saliva.
1) In most cases, IgA antibody began to be detected in saliva on the 4th day after the onset of disease and reached a titer of 1:8 or below, as measured by the indirect immunofluorescentt echnique. LgM antibody also appeared almost at the same time to reach a titer of 1:4 or below, but its persistence was shorter than that of IgA antibody. IgG antibody was detected from several cases, but titer was 1:2 or below and showed a tendency to disappear gradually.
2) Mumps virus was isolated from saliva until the 5th day after the onset of disease. In many cases the development of antibody coincided with the end of virus excretion.
3) Serum IgG antibody reached a titer of 1:128 or 1:512 in 4 cases. In these cases, however, no IgG antibody was detected in saliva. IgM antibody reached a titer of 1:16 or 1:32 in serum and titers of 1:2 and 1:4 in saliva in 2 cases. IgA antibody reached a titer of 1:8 or 1:16 in serum and a titer of 1:2 or 1:8 in saliva in all these cases.
4) Specific antibody was detected in parotid fluid which had been collected directly from Stensen's duct.
Because of the presence of antibody activity mainly in IgA, the coincidence of its development with the end of virus excretion, an very great difference in antibody response between saliva and serum, and the presence of antibody in protid fluid, the specific antibody was supposed to be produced in salivary glands by virus proliferation.
It was presumed that the antibody response of salivary glands might have an important role in the inhibition of growth of mumps virus and its excretion into saliva.

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Virologic and serologic studies were conducted on 23 cases of infectious mononuclesis-like illness in children. Of these cases, five were suspected to have been caused by cytomegalovirus six by EB virus. two by adenovirus, and two by cytomegalovirus or EB virus. The other 8 cases were induced by unknown etiology. The five cases caused by cytomegalovirus were below one year old, and displayed hepatosplenomegaly and liver dysfunction. The six cases caused by EB virus were all beyond one year old, and showed pharyngitis and lymphadenopathy.
These differences in clinical manifestations between the two viruses were coincident with those observed in infectious mononucleosis or cytomegalovirus-mononucleosis in American and European adults. Adenovirus and Toxoplasma were also suspected to be etiologic agents of infectious mononucleosis or mononucleosis-like illness.

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The enteric infection and the appearance of antibodies and immunoglobulins were examined in neonatally thymectomized germfree ICR mice.
Mouse adenovirus (MAD), strain K-87, was used in this study. Thymectomy was done within 24 hours after birth. MAD was inoculated orally to 4-to 6-week-old mice through a metal tube inserted into the stomach. The infectivity titer of the virus and the titer of neutralizing antibodies were determined in DKI mouse kindey tissue culture. Titration of the 3 classes of immunoglobulin was performed by the precipitation in agarose gel.
In unoperated control mice, no viral growth was seen 3 weeks after challenge. In the thymectomized mice, however, a clear prolongation of viral growth was observed.
Neutralizing antibodies in the serum began to increase in titer in the control mice 2 weeks after challenge. In the operated mice, the appearance of neutralizing antibodies was retarded. These antibodies in the intestinal wall and contents began to increase in titer in the control mice 3 weeks after challenge, but their appearance was retarded in the thymectomized mice.
Immunoglobulin examinations were carried out to clarify the status of IgA, IgG, and IgM.
The titers of IgA both in the serum and in the intestinal wall and contents were significantly lower in the thymectomized mice than in the control mice. IgG in the serum increased a little within the uninfected germfree mouse level in the control mice, but decreased in the thymectomized mice. IgM in the serum was within the uninfected germfree mouse level both in the control and in the thymectomized mice.
IgG and IgM in the intestinal wall and contents were undetectable both in the operated and in the unoperated mice.
Thus, prolonged growth of the virus was observed in the neonatally thymectomized germfree mice.
At the same time, the appearance of neutralizing antibodies both in the serum and in the intestinal wall and contents was retarded. As there was no correlation between viral growth and the presence of serum antibody, it seemed that the delayed appearance of local neutralizing antibody might have prolonged viral growth in the thymectomized mice.
Retardation of the appearance of IgA in the intestinal tract, which was undetectable in the uninfected germfree mice, was also observed in the thymectomized mice. This finding lends support to the presumption that the neutralizing antibody may belong to the IgG class of immunoglobulin.

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Rabbit antimouse antilymphocyte serum (ALS) was examined for effect on the time course of growth of mouse adenovirus strain K87 in oral infection. Four-week-old DK 1 inbred albino mice were used. At the same time examinations were carried out for the peripheral blood cells, the mouse adenovirus-nuetralizing substance, and the 3 classes of immunoglobulin, IgA, IgG, and IgM, in the small intestine, as well as in the serum, of the mouse. Sera were collected from four rabbits and pooled as an ALS, which was injected intraperitoneally in a dose of 0.15ml/head/day every day for 3 weeks. The results obtained are summarized as follows.
1) In ALS-treated mice, prolonged growth of the virus was observed distinctly, as compared with ALS-not-treated mice.
2) Peripheral small lymphocytes decreased in count especially with ALS treatment. After about a week of discontinuance of ALS treatment, however, the small-lymphocyte count returned to the level before the treatment.
3) No peripheral erythrocyte count decreased with ALS treatment. It seemed that the hemolysin-formation may have been prevented by the careful preparation of antigen cells.
4) In all the mice except a few, K87-neutralizing activity and immunoglobulin of the serum and small-intestinal wall and contents were at almost the same levels, regardless of the application or omission of ALS treatment. In several mice in which was observed prolongation of virus growth, the appearance of K87-neutralizing activity and IgA in the small-intestinal wall and contents was retarded in some cases or not retarded in others. It was suggested that the effect of humoral immunity might have induced the former cases and the effect of cell-mediated immunity the later.

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