Serological diagnosis of syphilis by means of agglutination test with Trejionema pallidum as the antigen was first attempted by one of the authors (Tani, 1938, 1940, 1948; Tani and Asano, 1951) . Nelson and Mayer (1949) reported the Treponezna pallidum immobilization test (T.P.I. test), which then was proven to be of comparatively high specific. Hence, interest was directed towards possibly more simplified agglutination test.
Treponema pallidumagglutination test (T. P.A, test) reported by the author was re-examined by Cain (1953), McLeod and Magnuson (1953), Hardy and Nell (1955), Meinicke (1956), and others.
In order to minimize the occurrence of spontaneous agglutination, Treponema pallidum was treated by antiformin (Tani, 1938, 1940, 1948; Tani and Asano, 1951) and later by bleaching powder (Tani, 1954) . The chlorine treated antigens, however, manifested 10 to 15 per cent spontaneous agglutination and retained the specificity for only a short period. Heat treated antigen, which had been reported to be satisfactorily specific, was also found to manifest approximately 10 per cent non-specific agglutination.
Meinicke (1956) stated in his review on the serological reactions for syphilis that T. P. A, test might not be acceptable as a very reliable reaction.
In the mean time, attempts were made to eliminate inert factors contained in serum samples in order to improve the specificity of T. P. A. test. Treatment of serum samples by hydrochloric acid, as reported by Sachs (1921) and Hayes and Sachs (1940), was found to contribute very much in improving the specificity of the reaction.
In the present paper, the experimental results on hydrochloric acid treated serum samples from various sources will be reported. For making comparison, the results with chlorine or heat treated antigens and simply inactivated serum samples, some of which were already reported elsewhere, will also be presented.

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As reported in the previous paper (Katsuyama and Kanai, 1958), the present authors have isolated two cell lines different in virulence by single cell culture from a human type strain of virulent tubercle bacilli (H2) . These two substrains were named H2Rv and H2Ra, the former being of high virulence and the latter being of low virulence in guinea pigs. In the present paper, further experiments will be reported to demonstrate the grade of virulence of H2Rv and H2Ra in more detail.

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Of the radioactive isotopes found to be present in the bodies of contaminated fish gathered by the survey ship“Shunkotsu Maru”in 1954, Zn-65 was quantitatively the highest (Kawabata, 1955; Yamada et al., 1955; Yoshii, 1955) . The enzyme, carbonic anhydrase, unicase and insulin are the major zinc-protein compounds. Numerous biochemical analyses of all types of tissue for the distribution of zinc, often with the aid of radioactive zinc-65 were reported. However, in spite of these extensive works, no histological study on the radiation injury of radioactive zinc-65 are presented.
The present work was undertaken to examine from the hi stol ogical view point the manifestations of injury caused by internal irradiation with zinc-65.

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As regards the food habit of the vector snail of Schistosoma japonicum, Oncomelania spp. only few reports are available (Izumi, 1951 ; Ritchie, 1955; Nanking Institute for Parasitology, 1956) . In order to observe the buccal activity of Oncomelania snail directly a simple technic is to be introduced here. By utilizing this technic a certain aspect of the food habit of Oncomelania is able to be elucidated. The mouth opening activity of the snail at that time was observed regardless of the existence of the feeding materials near the proboscis. This activity was named here as mouth opening reaction of Oncomelania. The frequency of this reaction per unit of time can also be utilized for the study of its food habit. Several environmental conditions under which this response is smoothly achieved were also examined.

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On the resistance of Oncomelania nosophora to dryness, several reports are available (Cort, 1919; Yamanouchi, 1919; Bartch, 1929; Sugiura, 1933; Kawamoto, 1954) . They all observed only their survival under the dried condition. Oncomelania nosophora, a Japanese vector snail of Schistosoma japonicum, however, has an amphibious character and can survive for a certain period under dried conditions. The effect of dryness on snails is considered to result in more evaporation of water from the snail body and inflict the gradual loss of water which would be the cause of their death. The purpose of this work is to know the relation between the rate of the water loss from snail body and the survival rate of the snail when put under a continuous dried condition.

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In the course of the study on the antibody response to human streptococcal infections, it was needed to prepare a standard antistreptolysin O and to establish a standard procedure for the measurement of antistreptolysin O (ASL) titer in human sera. As the first step of the investigation, the fundamental studies on measuring the hemolytic activity of streptolysin O (SL) were undertaken. As was performed by several investigators (Herbert, 1941; Gillen and Feldman, 1954; Halbert, Swick and Sonn, 1955), the 50% hemolysis end-point was determined by the spectrophotometric measurement, in order to achieve an accurate estimation of the hemolytic activity of SL. For setting up the standardized conditions, several variables which would influence HD₅₀ of SL were investigated in details.

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In the preceding paper (Kusama et al., 1958) on the spectrophotometric determination of the hemolytic activity of streptolysin O (SL), the effects of red blood cell concentration, cysteine concentration, stabilizing agent and incubation time on the hemolytic activity were investigated, and the standardized conditions for the measurement were established.
The present study deals with the neutralization reaction of SL by antistreptolysin O (ASL) in human, horse and immunized rabbit sera, under various experimental conditions. Several methods have been reported for the ASL titration of human sera by other workers (Todd, 1932; Hodge and Swift, 1933; Coburn and Pauli, 1935; Ipsen, 1944; Rantz and Randall, 1945; Kalbak, 1947; Robinson, 1951; Halbert, Swick and Sonn, 1955) . Most of them employed 15 minutes at 37°C for the combination of SL with ASL, and 45 minutes for hemolysis, using the complete inhibition of hemolysis or partial hemolysis (especially 50% hemolysis) as the end-point. Experiments to be described in this report were conducted mostly by testing varying amounts of serum against a constant dose of SL. Extensive investigations on such variables as the time for SL-ASL combination and the amount of the test dose of SL revealed the qualitative difference of ASL in sera from patients with streptococcal infections as well as those from healthy persons. Our standard ASL was produced by an improved method of titrating the ASL in human sera, being devised to overcome the difficulty due to this qualitative difference.

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In the previous reports (Kusama et al., 1958 a, b), the spectrophotometric determination of the hemolytic activity of streptolysin O (SL) and some fundamental aspects of the streptolysin O-antistreptolysin O reaction were presented. The qualitative difference of antistreptolysin O (ASL) in human sera, as manifested by different slopes of reaction curves and different combining velocities, was considered probably to be due to the avidity difference. A spectrophotometric method for the ASL titration which could minimize this qualitative difference by using a larger amount of SL than employed by other workers was described, and a standard ASL was prepared from a human serum with reference to the Danish standard ASL.
Since the spectrophotometric method is rather laborious and time-consuming, a simple method which could be suited for the routine diagnostic work is considered in this report.
The principle of the method is to compare visually the degree of hemolysis in a number of tubes containing known, varying amounts of the standard ASL with that in a dilution series of the unknown serum, using a constant dose of SL. A dilution of the unknown serum and a known amount of the standard ASL (expressed in units per cc), which would each cause 50% hemolysis, will be estimated by direct comparison or interpolation. Multiplying the former (the degree of dilution) by the latter (the number of units) will give the units of ASL per cc of the unknown serum.

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The agent of scrub typhus, Rickettsia orientalis, can be detected from the tissues of mice, rats, guinea pigs, and other experimental animals for a period of months after the acute manifestation of the infection had disappeared. On the other hand, it has already been proved that those animals once survived the infection ofRickettsia orientalisacquire a marked resistance to reinfection of the agent (Kohlset al., 1945; Fox, 1948; Smadelet al., 1949; Kouwenaar & Esseveld, 1949; Kuwata, 1952) . The resistance of these animals to reinfection may be directly or indirectly caused by the persistence of rickettsia in the tissues of those animals, namely, infection immunity or premunition (Parrot and Parrot, 1949) . Smadel et al. (1952) have shown thatRickettsia orientalispersists in the tissues of patients who recovered from scrub typhus for a considerable time, and found a certain correlation between the resistance of the individuals and the persistence of rickettsia in their tissues. Furthermore, this resistance manifests itself not only against homologous strain but also against heterologous strain for a long time, and he described that the resistance of an occasional individual to reinfection with a presumed heterologous strain after several years may depend upon the persistence in that person's body of viable rickettsiae and a resulting constant stimulation of his immune state.
In this paper, the authors present the results of their analysis of the resistance of mice, acquired from primary subcutaneous infection ofRickettsia orientalis (Kato strain) and manifesting against reinfection of the same agent by intraperitoneal route, and discuss the scrub typhus immunity in mice. The immunological differences in mice among many strains of Rickettsia orientalisnewly isolated in Japan will be discussed in the following (Shishidoet al., 1959) .

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Yamane reported that a growth stimulatory substance toMycobacterium tuberculosiswas isolated in a crystalline form from egg yolk (Yamane, 1958) . The present report deals with the chemical nature of this substance analyzing two different preparations provided by Dr. Yamane.
It was elucidated that this substance was a triglyceride. The effect of this substance in the medium could not be confirmed by many authors (Committee for Media of Tubercle Bacilli, 1958) .

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