As will be published later, A/Asia/1957 type influenza is thought to have entered Japan probably at the beginning of May, 1957. It spread then quite quickly from area to area within the country in spite of the season unfavorable to influenza infections, because the people had no antibody against this type of mutant virus. In this epidemic period a nursery in a suburbarn area of Tokyo City was involved in the epidemic. The present paper is devoted to the description of the epidemiological and clinical studies of the influenza outbreak in this nursery.

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Sodium pentachlorophanate (P.C.P. Na) is now considered as one of the most promising molluscicides. Field experiments with this compound against Oncomelania nosophora in Japan were reported by McMullen and others (1948; 1951), and Hunter and others (1952) . Since 1955 this compound has been used for practical molluscicidal purpose in the major endemic areas of schistosomiasis in Japan. In China, however, no application of this compound is yet found against Oncomelania hupensis, the vector snail of schistosomiasis in that country. They chiefly use B.H.C. and calcium arsenite for molluscicidal purpose. The latter compound was initially introduced as a molluscicide by the Chinese investigator (Su, 1954) and practically proved to be markedly effective. This compound acts as a food poison, and is now in practical use in the vast endemic areas in China.
The aim of this experiment is to examine the molluscicidal effect on O. hupensis of both compounds, P.C.P. Na and calcium arsenite, in the laboratory.

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This cercaria has been observed and described by earlier Japanese investigators. Initial report was made by Yoshida (1917), and two subsequent reports by Kobayashi (1918) and Ando (1918) . In 1922 Kobayashi summarized the above mentioned cercariae as “Cercaria flavopunctata B”, and Faust (1924) named it Cercaria pitta. Later on Takahashi (1929) proved that this cercaria developed to Stamnosoma armatus Tanabe, 1922, which was renamed as Centrocestus armatus by Yamaguti in 1933. Yamaguti (1938) also reported its detailed morphology with the confirmation of its life history.
A series of reports about the mucoid gland of American cercariae were published by Kruidenier (1951, etc.) . Recently Yokogawa and Yoshimura (1956) also reported about the mucoid gland of the cercaria of Japanese lung fluke, Paragonimus westermanii. The discovery of a series of metachromatic cells, so called “mucoid gland” in the cercariae by Kruidenier may help not only the study of the physiology of cercariae but also the evaluation of the classification and phylogeny of trematodes.
The authors had opportunities of getting the cercariae from the fresh water snails at several areas in Japan, and it was identified as the cercaria of Centrocestus armatus as a result of feeding experiments on gold fish. In the course of the investigation of the morphology of the cercariae, studies of “mucoid gland” were carried on. The followings are the detailed description of the morphology, especially of the mucoid gland of the cercaria, with a report of geographical distribution and its infection rate.

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The previous reports from this laboratory (Yoshino et al., 1956 a, 1956 b) indicated that both mouse passaged CVS and 7-day egg passaged Flury strains of rabies virus could infect the 1-day egg resulting in high viral concentrations in the embryo which were comparable to those usually reached in the infected mouse brain, and that these strains after adapted to the 1-day egg by serial passage could be satisfactorily titrated in 1-day eggs. This new titration method was especially of use for rabies virus, since the 1-day egg LD titration could be performed with more ease and shorter time than the conventional mouse infectivity test which had been the only method of titration available for this virus.
Meanwhile, Koprowski et al. (1954) found that 7-day egg passage of the Flury strain eventually produced a high egg passage (HEP) line which was unable to kill adult mice. The HEP Flury virus could be titrated by inoculation into baby mice, but there has been no other titration method for this particular virus routinely applicable in laboratory. Yet the use of baby mice has the disadvantage of occasional appearance of cannibalism, and therefore attempts were made here to adapt the HEP Flury virus to the 1-day egg with the expectation that it would become able to be titrated in 1-day eggs. When this attempt was started, however, a surprising fact was discovered that the HEP Flury virus, without any preliminary passage in 1-day eggs, was already as highly pathogenic to the 1-day egg as if it had received many previous 1-day egg passages. In the meantime, Takamatsu (1956) also passed Nishigahara strain in 7-day eggs for several years and reproduced the results of Koprowski et al. (1954), providing another HEP rabies virus. On examination of the pathogenicity for the 1-day egg of the HEP Nishigahara strain, we again found the same fact as revealed with the HEP Flury virus, i. e. it possessed high pathogenicity for the 1-day egg before any 1-day egg passages were tried.
Owing to this unexpectedly high pathogenicity for the 1-day egg of these HEP rabies viruses, they could easily be titrated in 1-day eggs, and as a consequence a way was opened for easy access to the biological properties. Detailed experi ments further demonstrated that these two HEP rabies viruses were not identical with each other in certain respects, and an analysis of the results obtained seemed to give a clue to solve the question of why and how the two different HEP viruses came to appearance, as will be stated in this communication.

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In our previous work (Yoshino et al., 1956 a), mouse fixed CVS as well as earlier 7-day egg passage of Flury strain showed nearly equal infective titers in both 1-day egg ID and mouse LD tests, but serial passage in 1-day eggs resulted in an increase approximately ten-foldly in the ratio of 1-day egg 1D to mouse LD titers. At first, it was expected that this difference between the two titers would become increasingly more pronounced as passages were repeated in 1-day eggs until finally the mouse infectivity would be lost. However, quite contrary to this expectation, the 1-day egg passage strains, COP and FOP, even after many passages through 1-day eggs did not alter this ratio and sustained as much infectivity for adult mice as did respective mother strains, CVS and Flury.
Then became important the question of whether or not one mouse LD (MIU) of the 1-day egg-adapted lines was equivalent to that of their mother viruses in terms of viral particle number. If one mouse LD of a mother strain represented N particles while that of its 1-day egg-adapted line corresponded to pN particles, a direct comparison of viral yields between these two viruses might be possible only after correction of the latter titer by the factor of p.
As was previously demonstrated (Yoshino et at., 1956 a), the peak viral concentration in the embryo obtained by the infection of 1-day eggs was as high as was reached in the mouse brain when both titers were expressed in terms of MIUs and therefore it was thought possible that more detailed investigations on the quantitative significance of MIU would revise our previous view concerning the viral yield in such young embryos. Approaches to this problem were quite difficult, because we had to resort only to indirect measurements of virus particles such as animal infectivity tests. However, the use of baby mice, which were found to be more susceptible than adult mice, and neutralization tests with a rabbit antiserum seemed to cast light on the solution of this problem. In order to avoid complexity, studies were confined to the relation between the mousefixed CVS and its 1-day egg passage line COP as a representative combination.
The results obtained appeared to point to an equal equivalence of MIU between these two viruses. It was also noticed that, in the ordinary titration employing adult mice, much of active virus was missed by detection even in the case of mouse-fixed strains, while the 1-day egg could be esteemed as one of the most sensitive hosts to detect active virus, at least for certain lines of rabies virus.

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Rabies virus has been known as one of the most cumbersome viruses in the attempts of in vitro cultivation. Kanazawa (1936) first succeeded in growing a fixed rabies strain in tissue culture with rabbit embryo brain, and similar results were obtained by Webster and Clow (1936), Webster (1937), Bernkopf and Kligler (1937), Schultz and Williams (1937-8) and Parker and Hollender (1945) using mouse embryo brain. Plotz and Reagan (1942) also passed two street virus strains in tissue culture employing whole chick embryo. However, no convincing evidence has ever been presented for success in cultivation of this virus without recourse to nervous tissues, despite the remarkable progress of tissue culture techniques during the last decade. Besides, the culture fluid in the above successful cases generally showed only low levels of viral yield, and reproducibility of those results seemed to vary greatly among different strains (Kanazawa, personal communication) .
Recently, Bequignon and coworkers (1954) observed maintenance over a period of 65 days of rabbit-fixed Pasteur strain in roller tube cultures employing mouse embryo brain, and stated that the fibroblastic outgrowth seemed to produce virus without showing any cytopathic changes. Unfortunately, however, these results could not be reproduced in our hands with our mouse-fixed strains, nor with their street virus (Vienchange et al., 1956) . Also recently, Kanazawa (personal communication) could pass egg-adapted Nishigahara strain in tissue culture with chick embryo cells, but fairly luxuriant virus growth was seen only in the first few passages. With the same technique, however, we could not obtain any growth of the egg-adapted Flury strain. Thus, a time has not yet come when tissue culture virus can be commonly used as a source of vaccine, although earlier data given by Webster and Clow (1936), Kligler and Bernkopf (1938) and Webster (1938) cast promissing light on such practical application of culture virus.
In the meantime, it was found here that two strains of rabies virus, mouse-fixed CVS and early egg passage of Flury, could readily grow in 1-day eggs (Yoshino et al., 1956 a) and that adult-mouse-non-pathogenic HEP (high egg passage) rabies viruses were rather more infective to 1-day eggs (Kuma, 1958) . These discoveries, coupled by the information that the 1-day egg whose egg-white was replaced with saline could serve as a new type of tissue culture for herpes simplex virus (Yoshino and Taniguchi, 1957), led the authors to the attempt to cultivate the above strains of rabies virus in the egg-white-replaced 1-day egg (ERO), with the result that sufficient growth in the blastodermal tissues as well as release into saline of these viruses was observed. In addition, 1-day egg-adapted lines of these strains produced by serial 1-day egg passage were also grown in this culture system in comparison with their respective mother strains. Of course, the present ERO culture method is by no means perfectly satisfactory, but the results to be reported will suggest that the ERO is applicable not only for the practical purposes such as vaccine production but also for some theoretical studies of the host-virus interactions.

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The technic of tissue culture has recently been improved so much that some cell lines can be carried in just the same manner as bacterial cultures. Siminovitch et al. (1957) showed that the growth mode of the L strain cells cultivated in suspension resembled those of bacteria. The HeLa strain cells which grow adhering to the bottom of culture flask were proved to have 3 phases, namely lag, logarithmic and stationary, during their growth (Yamada et al., 1956) . While it is known that bacterial cells change their physiological activities according to growth phases, no such kinetic observation has been made on animal cells in tissue culture. There are some reports (Warburg, 1955; Leslie et al., 1956; Phillips and Feldhaus, 1956; Phillips and Mc Carthy, 1956) on the metabolism of animal cells cultivated in vitro in respect to their malignancy. These findings, however, cannot be compared with those obtained on tissues in vivo with balanced nutrition and discharge, because it is obvious that the cells growing in vitro produce some changes in the closed environmental condition which in turn affect the physiological activities of the cells. The physiological activities of the cells in vitro, therefore, should be pursued throughout the process of their changes during the cell growth.
In the present study, the changes in endogenous respiration and anaerobic glycolysis of the HeLa strain cells were pursued through the course of their growth. It was observed that the utility rate of respiration was higher at the earlier stage and that of glycolysis increased as the cells grew. Those changes are considered to be due to the characters of the cells affected by the environmental condition in vitro.

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