The systolic blood pressures in six strains of rats including SHR were measured using the tail water plethysmographic method on fifteen weeks of age. The blood pressure of SHR strain was distinctly higher than those of other five normotensive strains. A small but clear difference could be observed among the blood pressures of normotensive strains. Sex difference was obser ved in all strains.
The degree of genetic determination calculated from the F₁ and F₂ data between Wister-Imami-chi and SHR strains was 63.7±12.5 percent in females and 62.4±12.3 percent in males. The result indicated that the high blood pressure in SHR strain is a highly heritable trait. Sex difference was also observed in each generation.

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The influence of environmental conditions in the long-term care of SPF rats was studied under three different systems. No statistical differences were recognized on growth curves, several clinical laboratory tests, organ weights and histopathological observations in the rats maintained for 8 months under the environment of SPF system and semi-clean system. However, under the conventional environment, pneumonia was observed in a few rats within 1 month, and growth of the rats delayed as compared with that under SPF and semi-clean systems.
Bacterial flora in the rat faeces did not differ during 3 months among the three systems, though Gram-positive bacilli were detected only in the faeces of the rats fed with non-sterilized diets. In conclusion, practical maintenance of SPF rats was considered to be possible under the semi-clean system.

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The heart and great vessels of Wistar and Sprague-Dawley (SD) rat fetuses at term were examined by the free hand razor blade section method. To detect a small defect the blood filling the aorta and the left ventricle was removed from the level just above the aortic valve to the upper muscular portion of the left side of the septum. Spontaneous interventricular septal defects were detected in the upper (type A), middle (type B) or lower (type C) membranous part, or in the muscular part (type D) . The overall prevalence of interventricular septal defects was 3.9% in the untreated Wistar 3.1% in the Wistar given 0.5% CMC solution on day 10 of gestation, 5.2% in the untreated SD and 3.6% in the CMC treated SD. The type D defect was found only in the Wistar fetuses. In addition to the septal defect, right aortic arch was observed in the Wistar fetuses. Comparison between the present data and the previously reported figures revealed no indication of a lesser degree of ac-curacy in detecting interventricular septal defe cts with the authors' technique.

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In general, most of the monkeys used for biomedical research purposes are not yet laboratorybred animals but in-nature bred ones even today. Thus, when we import them to use as experimental animals, we have to take it into consideration that the health condition of the monkeys may be fluctuated with the alteration of various environmental factors including diet during and after importation from the natural habitat.
With regard to the nutritional condition of cynomolgus monkeys imported from Southeast Asia, we used to classify it into the following four grades after observation and palpation of general physical appearance, for example, tension of the skin, luster of the hair and slenderness of the body etc.. The first grade is “good” nutritional condition, being expressed by a symbol, (+) ; the second grade, “ordinary”, (±) ; the third grade, “a little bad”, (±), and the fourth, “extremely bad”, (-) .
In the present report, mortality, body weight gain and change of the grade of nutritional condition during the quarantine period of about 6 weeks were statistically analyzed according to the nutritional grade judged at the time of arrival at our monkey facility. Then some hematological determinations including hematocrit value, white blood cell count and serum total protein content, and estimations of serum-and tissue vitamin C level were made on 133 cynomolgus monkeys near the end of the quarantine. period. Also these hematological data were compared with each other according to the nutritional grade judged at the time of these examinations.
The results obtained are as follows :
I. The statistical analysis of monkeys imported from 1965 through 1969 showed that the worse the grade of nutritional condition judged at the time of arrival, the higher the mortality during the quarantine period, as well as, the higher the rate of body weight gain (Tables 3, 4) .
The improvement of nutritional condition which is expressed as the change of the nutritional grade from the lower to the higher during the quarantine period, was observed in 34% of 700 monkeys surveyed. And the same grade was maintained in 50.3% of them throughout the quarantine period (Table 5) .
II. Statistically significant higher levels of average hematocrit value, white blood cell count and serum total protein content were observed (P=0.05) in the groups of monkeys having the higher two grades of nutritional condition, compared with the groups having the lower two grades (Table 6, Fig. 1) . That is, groups of monkeys having lower grades, more of less, suffer from anemia, leucopenia and hypoproteinemia.
Average serum vitamin C level was almost the same in every group of the nutritional grade (P>0.05) . In addition, no statistically significant difference of the average value of the intra-dermal vitamin C test or the lingual vitamin C test was seen among the groups (P>0.05) (Table 6, Fig. 1) . That is, about the same levels of vitamin C intake with food and of vitamin C accumulation in tissues were confirmed in each grade group.
The present results seem to indicate that the routine feeding system of our laboratory, including dietary care, is practically suitable for cynomolgus monkeys kept for some experimental purposes, and that our empirical criteria of the nutritional condition of cynomolgus monkeys can be useful when we check the bad nutritional condition showing anemia, leucocytopenia, and hypoproteinemia, but is not effective for the judgement of nutritional condition derived from vitamin C deficiency.

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Rhythmic phenomena, concerned with circadian, lunar or seasonal cycles, in the living organisms have widely claimed the attention of biologists. In this paper, a rhythm different from these cycles in rodents is described. This rhythm was noted unexpectedly in the course of studying the mechanism of the cecal enlargement in the penicillin-administered rat.
Water intake by a mouse reared in a room with a dim illumination in the daytime from 9 : 00 to 18: 00 and without from 18: 00 to 9 : 00 in the next morning, was recorded by the equipment illustrated in Fig. 1. The diurnal rhythm of its water intake, being more and oftener on hour basis in the dark environment, has been maintained after switching to the all day dim illumination as shown in Fig. 2. However, as given in Fig. 3, the rhythmic cycle of about 20 days was found in mice by the long-term observation on the water intake rate in the daytime (WRD) which was calculated from the following formula;
WRD=Volume of water intake in the daytime/Volume of water intake in all day
×100 (%)
The rhythm in rats had smaller amplitude and some longer cycle than that of mice.

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This paper mentions three frequently used methods for estimating the incidence of spontaneous tumors in experimental animals described by Varma, i. e. naive method, overall effective number method and modified life table (actuarial) method.
Incidence of spontaneous mammary tumors in strain DD mice is estamated by these methods, and discussion is made on the cause of different incidences obtained.

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The normal growths of spontaneous mammary tumors in mice were investigated. All the mice were checked for palpable mammary tumors once a week in their life spans. The tumor size was expressed as the geometrical mean of the major two diameters of each tumor.
The general features of mammary tumorigenesis of mice used in the present experiment are illustrated in Tables 1 and 2. In the spontaneous mammary tumors of mice with only one tumor each in their life spans, there were no differences in their growths between nullipara and multipara in both C3H/He and Swiss albino mice. The tumor growth was generally faster in C3H/He mice than in Swiss albino mice (Fig. 1) . In the spontaneous mammary tumors in mice with two tumors each in their life spans, little differences in the growth were observed between the first and the second tumors in nullipara, although the tumor growth was much retarded in Swiss albino mice. On the other hand, the growth of the first tumor was slower than that of the second tumor in multipara, especially in C3H/He mice (Fig. 2) .
The significance of these findings was discussed.

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