Stewart, Robert B. (University of Rochester, Rochester, N. Y.). Growth and lethal effects of the psittacosis agent in chicken embryos of different ages. J. Bacteriol. 83:423-428. 1962.-Inoculation of the psittacosis agent (strain 6BC) into the yolk sacs of chicken eggs in different stages of embryonic development resulted in a steady decrease in ld(50) titer as the embryos increased in age from 7 to 10 days. Correlated with the decreased ld(50) titers in older eggs was the finding that the titers of the organism were lower in the yolk-sac tissues of the older eggs. The embryos themselves also gained appreciably in resistance with increase in age, since comparable titers of psittacosis organisms were found in embryonic tissues of differing ages at the time of inoculation but the mortality of older embryos was considerably less. This resistance of older embryos to the lethal effects of the psittacosis agent could not be demonstrated when the organism was introduced intravenously instead of into the yolk sac.

Although the findings from the study were not statistically significant, they can be seen as clinically significant in terms of patient comfort and reduced dependency in care by a reduction of time with a tracheostomy. It is recommended that a larger scale study be carried out to determine if a tracheostomy weaning protocol does make an impact on length of time to extubation in wider care settings.

4-NITROQUINOLINE N-oxide (NQO), which was already known to have antifungal and mutagenic activity, was first shown to be carcinogenic by Nakahara, Fukuoka and Sugimura (1957). These authors applied the compound to the skin of 20 mixed strain mice and obtained tumours on each of the 14 which survived more than 100 days. Rather unexpectedly, the tumours on 4 of these mice were found to be sarcomas, though some difficulty was experienced in determining their exact cell type. Differences in the degree of incidental surface erosion were suggested to account for thQ production of carcinomas on some mice and sarcomas on others.The carcinogenicity of NQO for mouse skin has also been investigated by Lacassagne, Buu-Hoi and Zajdela (1961). They reported a strain difference in response to NQO, papillomas and epitheliomas being produced on their C57B1/Z mice but not on XVIInc/Z mice. However, their ascribing this effect to possible differences in the SH-content of epidermal cells of the two strains appeared to us unjustified on the evidence available, since these workers also described severe toxic reactions to the NQO applications, which resulted in progressive emaciation, cachexia and death of many mice without the production of tumours. Nakahara et al. (1957) only applied very small amounts of NQO (about 0.02 ml. of a 0-25 per cent solution in benzene 3 times a week), but their loss of 6 out of 20 mice during the first 100 days of treatment is also suggestive of marked toxicity.The present paper summarises the results of a number of separate experiments with NQO carried out in our laboratories using both random-bred mice and pure-line mice of several strains. The first experiments (I-III), using random-bred stock albinos and C57B1 x IF F1 hybrids, demonstrated toxic effects of NQO similar to those described by the earlier workers, and we also obtained some sarcomas in addition to papillomas and carcinomas. Another series of tests was then carried out in which smaller amounts of NQO were applied to the skin of these mice and of four pure-line strains of mouse, with a view to elucidating the question of strain differences in response to NQO under conditions of reduced toxicity (Experiment IV). This experiment demonstrated marked strain differences in the toxic and carcinogenic effects of NQO. Moreover, it was unexpectedly found that in some strains of mouse, sarcomas were induced in larger numbers than epithelial tumours. A further experiment (V) with one of these strains is also included in this report.

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SUMMARY This technique enables small specimens for electron microscopy to be obtained from specific zones of large pieces of tissue. The method depends on the use of frozen sections, for localization of histological features, but circumvents the risk of ice‐crystal damage to the specimens selected.