The Growth of Various Species of Bacteria and Other Micro-Organisms in Atmospheres Enriched with Oxygen.
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In a previous paper,2 we have described experiments showing that the Bacillus tuberculosis will only grow between certain percentages of oxygen in the atmosphere to which it is exposed, and is killed either by absence of oxygeni or by over eighty per cent. of oxygen. In other words, a partial pressure of oxygeni of about 600 mii. of mercury is fatal to Bac'illus tuberculosi's equally with a very low pressure. It was also founid that such a higlh oxygen pressure stopped the growth of the organisn Staphylococcus pyogenes aureus, and usually conasiderably inhibited, or stopped in some cases, that of S. albus; the third organism of this group, S. citreus, was less obviously affected. Only twice lhave we obtained a fair growth of S. auireus in increased oxygen; as a rule, the colntrast between the control tubes grown in air and the oxygeni-growni tubes is most striking, the oxygen-grown tubes appearing to be quite sterile, wlhile the others show a luxuriant growth. There was this important differenice, however, that the B. tuberculosis was killed outright by the oxygen, the small patches of started growths having turned dark brown at the emid of the more prolonged period of about two to tlhree weeks necessarv to test the culture of this niore slowly growinig org,aniism, while the cointrols were wlhite anid flourishing. On the other hand, at the enid of the slhorter period of onie to two days necessary to test the culture of the Staphylococei, altihough the oxygen tubes had not grown, if they were niow transferred to ordiniary air a fairly good growth was obtainied. In the former paper a fair inumnber of otlier organisms were similarly tested, suclh as B. coli, B. typhosus, B. pyocyaneus, B. dysenteriae