Simultaneous administration of dehydroacetic acid inhibited or delayed the induction of the hepatomas in rats fed 4-(dimethylamino)azobenzene (DAB). Neither hepatomas nor liver cirrhosis was found in a group of rats fed a diet containing 0.25% dehydroacetic acid, in addition to 0.06% DAB, for 173 days and succeedingly fed basal diet for 77 days, although atypical proliferations of hepatic cells were found in about 3/5 of 16 rats and an adenoma in one rat. In an attempt to elucidate the mechanism of this inhibitory effect of dehydroacetic acid, effect of dehydroacetic acid on the liver microsomal enzyme activity for metabolizing azo dyes and on the protein-bound dye was examined throughout the term of the carcinogenesis. Dehydroacetic acid increased the microsomal enzyme activity like other inhibitors such as riboflavin and 3-methylcholanthrene, when dehydroacetic acid was given to rats singly. However, this increasing activity of dehydroacetic acid was comparatively weak and was made negligible by simultaneous administration of DAB which decreased the microsomal enzyme activity. From this fact and other findings, which suggested that dehydroacetic acid did not affect the concentration of DAB in animal tissues and organs, dehydroacetic acid could be considered to inhibit the induction of hepatomas not by accelerating metabolism of azo dyes. On the contrary, dehydroacetic acid inhibited the formation of the protein-bound dye, in the microsomal and the supernatant fractions of the liver homogenate, in the early stage of carcinogenesis, and delayed the decrease in the ability of liver to form the protein-bound dye, especially in proteins of the supernatant fraction of the liver homogenate, at a later stage when hepatomas appeared. A parallel relationship was obtained between the effect of dehydroacetic acid on the protein-bound dye and the inhibitory effect of dehydroacetic acid on the induction of hepatomas.

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In this series of experiments the influence of oxygen at high pressure (3 atmospheres absolute) on the growth of cells was investigated, using HeLa, FL, and Yoshida sarcoma cells. The inhibitory effect of oxygen at high pressure on the propagation of cells was considerably severe and highly significant compared with those on other groups, which were exposed to oxygen at atmospheric pressure, air at 3 atmospheres absolute, and air at atmospheric pressure. The relationships among the experimental groups exposed to various conditions of oxygen treatment for 24 hours were of great interest. The results obtained here indicate that the influence of oxygen at high pressure on the proliferation of Yoshida sarcoma cells is more severe than that on two established cell lines.

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Lymphoid cells in regional lymph nodes of mice bearing Ehrlich ascites cell tumor have some cytocidal action on cultured Ehrlich ascites carcinoma cells. The regional lymph node protein was fractionated on Sephadex G-200 column and on DEAE-Sephadex A-50 column. The antitumor activity was determined by cell culture test. The antitumor activity was mainly present in the fraction with β-mobility from DEAE-Sephadex A-50 column chromatography. The sedimentation coefficient of this protein was 6.5S. This protein was soluble and permeable through a cell-impermeable diffusion chamber. The minimum protein concentration required for suppression of tumor cell growth was about 300μg for 10⁴ cultured JTC-11 cells in 10ml culture vessel. In electrophoresis, this fraction moved mainly to β-position, and contained a small amount of α-band. The antibody in regional lymph node was loaded mainly on β- and α-mobility protein.

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Treatment of Ehrlich carcinoma Line-17) with Proteus mirabilis RMS 203 (Murata strain) was effective following daily, intermittent, or single intravenous injections. Gross necrosis in tumor tissue was induced within a few days after administration of P. mirabilis and led to significant reduction of tumor size. Whereas some of the tumors of various sizes completely regressed after necrosis occurred following injection of the bacteria, the percentage of complete regression was the highest among tumors which were approximately 11mm in diameter at the start of treatment.
The effects of 1×10⁹cells/kg of P. mirabilis on 17 other transplantable mouse and rat tumor systems were also studied. Necrosis was observed in the majority of the tumors. Complete tumor regression occurred in 11 tumor systems, the greatest percentage (>70%) being in sarcoma-37.

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Of undifferentiated carcinoma of the lung, oat-cell type is peculiar in that it is clinically very malignant and the serotonin level in the serum may be high, but agreement is yet to be reached on its histological classification and histogenesis.
Nine cases of oat-cell carcinoma and one case of bronchial carcinoid which developed in the larger bronchi were studied by electron microscopy and biochemically. Within the scope of the present experiments, it has been clarified that most of oat-cell carcinoma is a specific lung cancer containing serotonin granules, developing from argentaffin cells found in the bronchial mucus glands.

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The effect of oral administration of 0.08% 4-aminoazobenzene (AB), 0.09% 3-methoxy-4-aminoazobenzene (3-MeO-AB), 0.1% 3, 4'-dimethoxy-4-aminoazobenzene (3, 4'-(MeO)₂-AB), 0.09% 4-monomethyl- and 4-(dimethylamino)azobenzene (MAB and DAB) in the diet was studied in Donryu male rats with special reference to their carcinogenicity, target organs, as well as the histopathology of the induced tumors.
1) AB did not cause any cancerous change in any organs excepting in one rat in which a fibrosarcomatous nodule, covered by the omentum and mesenterium, was found.
2) MAB and DAB produced tumors in the liver alone. Histologically, these were poorly differentiated hepatocarcinoma and transitional type between hepato- and cholangio-cellular carcinoma.
3) 3-MeO-AB produced well-differentiated hepatocarcinoma, malignant hemangiopericytoma of the spleen, and squamous cell carcinoma of the ear duct in 21(91%), 6(26%), and 2(8%), respectively, out of 23 rats.
4) 3, 4'-(MeO)₂-AB developed well-differentiated hepatocarcinoma, squamous cell carcinoma of the ear duct, and tubulary adenocarcinoma of the small intestine in 24(100%), 1(4%), and 2(8%), respectively, out of 24 rats.
5) The average time for tumor development was shorter in MAB and DAB groups than in 3-MeO- and 3, 4'-(MeO)₂-AB groups.

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Twelve tumors of the thymus were observed in 120 tumor-bearing mastomys out of 157 untreated animals autopsied; 5 epithelial cell-type tumors, 4 lymphoid cell type, and 3 mixed type tumors, according to our classification. Distant metastasis and invasive growth were observed in 3 cases.

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A distinct nucleolar morphological change in hepatic parenchymal cells was observed following the intraperitoneal injection of dimethyinitrosamine into C57 male mice. On supravital staining with Azure C, the change was manifested by a clear-cut separation of the azurophilic and non-azurophilic components.

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Water extracts of some wild Basidiomycetes were tested as to their antitumor action using sarcoma-180. Material from P. linteus by ethanol precipitation and dialysis highly inhibited the growth of the tumor.

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Water and alkaline extracts were prepared from nine species of wild Basidiomycetes, and their inhibitory effect on sarcoma-180 was tested. Some extracts were found to be highly effective. The active components would be macromolecular compounds.

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Thirty rabbits received the subcutaneous injections of 4-nitroquinoline 1-oxide in a mixture of olive oil and cholesterol. Lung cancer occurred in 4 out of 7 effective number of animals surviving more than 960 days after the injection. Cancers were diagnosed as well- and undifferentiated adenocarcinomas and largecell carcinomas with giant cells. One of them had an endometrial carcinoma.

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In order to ascertain whether tumor ascites might contain tolerance-inducing agents, grafting of allogeneic skin was performed on mice which were receiving daily administration of xenogeneic or syngeneic cancerous ascites. The result was determined by the survival time of grafted skin. No modification, however, in the skin graft rejection was demonstrated by this treatment.

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