The relative absence of saprophytism in freshly isolated strains of Bacillus abortus is conveniently measured by inoculating a series of agar tubes with. successive dilutions of culture and sealing the tubes. The appearance of films of growth is delayed from 3 to 17 days and suppressed with the increase in the dilutions. As many as 100,000 bacteria per sq. cm. of agar surface are suppressed. When the confined air contains CO2 in a concentration as low as ¼ per cent and up to 10 per cent, the inhibition and suppression do not occur. Concentrations down to 0.1 per cent are still capable, even though in a slightly retarded manner, of bringing high dilutions into growth. In all cases the resulting growth was remarkably vigorous when compared with that in sealed tubes.

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