Bowman's capsules with cuboidal epithelium were found in 87.2%, 95.5%, 75.4%, 96.7%, 98.8% and 91.2% in the kidney of adult male C57BL/6J-ob, JCL-ICR, dd, E1, ASK and KK mice, respectively, while in 57.9%, 6.7%, 7.0%, 2.8% and 9.1% in adult female C57BL/6J-ob, JCL-ICR, dd, El and ASK mice, respectively. The renal corpuscles with cuboidal epithelium in Bowman's capsules of male JCL-ICR mice increased gradually in number from 5 to 10 weeks age. The surface of cuboidal epithelium cells was shown to have long cilia and dense microvilli, which were similar to those seen in proximal uriniferous tubules.

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A colony of rabbits free from coccidia was established in 1974 by weaning young at 25 days of age from dams infected with coccidia. Until now Bordetella, Pasteurella and Psoroptes cuniculi have not been detected either, and neither diarrhea nor death has occurred in weanlings of the colony. However, the mortality of sucklings was significantly high owing to cannibalism and tread by their dams. The weaning rate was effectively improved by use of a large nursing cage (3, 100cm²) and sterilized hay on a stainless steel mesh floor of the nursing cage.

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For period from 1971 to 1975, 18 cases of osteosarcoma were experienced among 9132 spontaneously hypertensive rats. The onset was at 72 to 145 days of age and death occurred before 423 days of age. The tumors were multiple being distributed in the skull (11 of 14 cases), caudal vertebrae (8 of 14 cases), and fore- and hind-limb. All the tumors were mainly composed of sarcomatous tissue with some osteoid and cartilage. Metastasis was never observed. Serum Al-P levels of tumor bearing animals were 2 times higher than those without tumor. Bronchiectasis and abscess formation of submaxillary lymph nodes were noted in most affected animals.

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The present study was performed in order to elucidate the effect of proximate environment on drug susceptibility of mice. Three experiments were carried out independently. In the first experiment, mongrel and ddS mice produced under an unsatisfactory control of proximate environment were purchased, and acute toxicity tests of thiamine hydrochloride (B₁HCl) and isonicotinic acid hydrazide (INAH) were practiced at two different conditioned rooms. In the second experiment, ddY mice produced under the conventional environment controlled to a certain extent were purchased, and the toxic effect of B₁HCl was examined under the similar environment. In the third experiment, the sensitivity to B₁HCl of RFVL mice produced under the strict barrier system was tested at the severe air-conditioned room. LD₅₀ and their fLD₅₀ values were calculated by Litchfield-Wilcoxon's method, and the variance analyses were carried out. The severer the environmental control after the purchase of mice turned to the higher the drug sensitivity. This respect was more remarkable in INAH of which the toxic response is appeared slowly compared with B₁HCl. Furthermore, seasonal variation was found in LD₅₀ values. However, seasonal effect differed from rearing and experimental conditions. In the third experiment which these proximate environments were controlled severely, seasonal variation was very small. From the results of these experiments, it was defined that the use of animals produced under the satisfactory rearing condition and severe environmental control are necessary for animal experiments.

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Genetic control of blood pressure in the SHR strain was studied by three separate experiments which consist of cross analysis between the SHR and Donryu, two-way selection for high and low blood pressure levels, and successive back-crosses to the parental strains. The results obtained were as follows.
1. The data from genetic crosses between the SHR and Donryu showed the phenotypic segregation ratio of 1 : 1 at the backcross and 1 : 2 : 1 at the F₂ generation.
2. Two-way selection for high and low blood pressure levels was performed from the F₂ generation onward. The separation between the two lines occurred immediately after the first selection. Thereafter, the difference increased gradually with generation. The blood pressure level at the seventh generation of selection became approximately equal to those of the parental strains.
3. Two types of the successive backcross were performed from the F₁ hybrids by mating the males showing the highest blood pressure level to Donryu females and the females showing the lowest blood pressure level to SHR males on the other. Bimodality was observed in the distribution of blood pressure levels at each generation. Their phenotypic segregation ratios were accordant with 1: 1 on the whole. At the intercross generation during successive backcrosses, a trimodal distribution was observed.
4. These results confirmed that the hypertensive trait of the SHR is regulated by a single major gene and other several genes with minor effect. A gene symbol ht was proposed for this major gene. Concurrently, a congenic strain having the ht gene on the genetic background of the Donryu was developed by the successive backcross system.

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Increase of lactate dehydrogenase (EC 1.1. 1.28) and creatine kinase (EC 2.7. 3. 2) in serum and plasma level during blood clotting was compared in R. rattus flavitectus (black rat) and R. norvegicus (albino rat) . Both the enzyme level increased by the release from platelets in process of clotting in rat as previously described (Emori T., Takahashi M. and Nagase S. (1978) Exp. Animals, 27, 167), but the change in black rat was very slight.
Owing to search for the reason to prove the difference in this phenomenon, physiological and chemical properties of blood from both the animals were compared, and it was demonstrated that the content of plasma fibrinogen in black rat is higher than that in albino rat, while the platelet number contained in each ml of blood and the enzyme activities in each platelet are not different between them. The analysis of the membrane proteins from platelets of both the animals by SDS-polyacrylamide gel electrophoresis showed that the fractional value of glycoproteins was found to be different between them.

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Fatal herpesvirus tamarinus infection was observed in cotton-topped marmosets (Saguinus oedipus) imported from South America via the United States on August 26, 1976. In addition to the lesions hitherto reported in herpesvirus tamarinus infection, severe degenerative and necrotic changes of ganglion cells were recognized with intranuclear inclusion bodies in the plexus of the digestive tract and the sympathetic nerves and their ganglions in the abdominal cavity. Inflammatory or regressive changes were also noted in the central nervous system. A large number of basophilic or eosinophilic intranuclear inclusion bodies frequently recognized in multinucleated giant cells were observed in various organs and tissues, and they showed different shapes at the electron microscopic level. Morphological findings indicated that herpsevirus tamarinus infection seemed to be similar to herpes simplex virus infection in man. The findings of the susceptibility of a variety of cell cultures to the virus isolate serologically identified as herpesvirus tamarinus and physicochemical characteristics of the virus isolate were in general agreement with the findings of herpesvirus tamarinus already reported by previous workers.

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A new, simple and inexpensive instrument, that proved to be useful for perfusion fixation of small laboratory animals, was devised.

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The age-related incidences and types of spontaneous tumors were studied in 320 male and 354 female Wistar-Imamichi rats reared up to 130 weeks of age. The tumor incidence increased abruptly between 53 and 78 weeks of age, and 170 males and 269 females were shown to bear tumors during the observation period. Multiple tumors occurred in 62 males and 115 females. Most common were hypophyseal ( _??_ 69 : _??_ 224), mammary gland (29 : 99), testicular (74 : 0) and adrenal gland (26 : 21) tumors. The incidences of hypophyseal and testicular tumors increased with age. Tumors occurred in later stages of the observation period in the ovary, uterus and vagina (0 : 27), thyroid and parathyroid (13 : 12), skin (8 : 8), spleen and lymph nodes (8 : 7), pancreas (9 : 5), liver (3 : 7), lung (3 : 3), thymus (1 : 4), omentum and mesenterium (2 : 3), stomach and intestine (2 : 2), kidney and urinary bladder (1 : 2), right femur (0 : 1), and brain (0 : 1) .

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A basal stock of Swiss albino mice was selected to two ways for high and low mammary tumorigenesis and two new strains were established (SHN and SLN) [27, 34] . They have still been selected and maintained by the strict brother×sister mating. SHN and SLN are now at F37 and F31, respectively.
In this paper, the changes in mammary tumorigenesis in both strains until F30 and the strain-difference in several characteristics concerning mammary tumorigenesis were briefly reviewed.
Mammary tumor incidence was increased and onset age of tumors was decreased with the advance of generation in SHN breeders and they were almost constantly 100% and 6-7 months, respectively, after F11. The effects of selection were not so marked in SLN breeders; mammary tumor incidence was fluctuate largely around the mean value of P generation and increased considerably after F23. The onset age of tumors became about 1 month later than P generation on average (Fig. 1) .
SHN virgins showed mammary tumor incidence of more than 90% and the onset age of 8-9 months. The effect of selection in SLN females was marked in virgins and the incidence and the onset age were 10-20% and 14-18 months, respectively, in each generation (Fig. 2) .
While the life spans of breeders and virgins which died without mammary tumors were 8-14 months and 13-19 months, respectively, in both strains, the variations were so large in each generation.
All mammary tumors checked were diagnosed as adenocarcinoma and the number of tumors per mouse was significantly higher in SHN than in SLN. The tumors of both strains were hormone independent (Fig. 3) [21], and the growth potential of tumors was higher in SHN than in SLN when transplanted into female nude mice (Fig. 4) .
While 1 out of 39 (2.6%) mammary tumor bearing SHN mice had metastases to the lung, the ratio increased up to 23% (10/43) by elongation of survival time of animals by surgical removal of mammary tumors.
Both normal mammary growth (Fig. 6) and preneoplastic mammary hyperplastic alveolar nodule (HAN) formation (Fig. 7) were much more marked in SHN than in SLN.
SHN was superior to SLN in mammary sensitivity to prolactin and ovarian hormones, whereas no clear differences between strains were observed in plasma prolactin levels at different reproductive states (Fig. 8) [15, 27] or mammary gland prolactin receptor during lactation [15] .
The pattern of estrous cycles of SHN females was characteristic in having long continued diestrous phases (Fig. 9) [24] . Among several characteristics examined as the indices of reproductivity (Fig. 10), characteristics concerning lactational performance, litter growth and litter growth rate, became better with the advance of selection in SHN (Fig. 10-E, F, G, H) .
The mammary tumor appearance was much higher and earlier in (SHN×SLN) F1 virgins than in (SLN×SHN) F1 virgins (Fig. 11), indicating higher mammary tumor virus (MTV) activity in SHN than in SLN. MTV antigen was identified by immunodiff usion test in the milk of both SHN (100%) and SLN (83%) [2] . It was also found in prostates and seminal vesicles of males of both strains [36] .
The responses of normal spleen cells and that of fat pad to PHA were significantly lower and higher, respectively, in SHN than in SLN.

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