The Proportion of Viable Bacilli in Agar Cultures ofB. aertrycke(Mutton), with special reference to the change in size of the Organisms during growth, and in the Opacity to which they give rise

Abstract

1. Working with agar cultures of a strain ofB. aertrycke(mutton) it was found that the number of organisms requisite to cause a given opacity was five times as great in a 26-hour as in a 4-hour culture.2. This difference is probably explicable by the fact that bacilli from young cultures are larger than those from old ones.3. Evidence is produced which suggests that the opacity method gives a measure not of the number of organisms, but of the total quantity of bacterial protoplasm in the suspension. It should therefore be of special value in the standardisation of vaccines.4. It is pointed out that the opacity method when used for the enumeration of bacteria is subject to a considerable error, and is hence unsuitable for accurate work.5. A technique is described for the estimation of the proportion of viable to total organisms in an agar culture.6. The results obtained are closely similar to those already described for broth cultures.7. The maximum proportion of living bacilli is reached at the end of the logarithmic phase of growth, when about 80 per cent, of the organisms are alive and capable of reproduction.8. It seems probable that there is a mortality amongst the bacilli that are generated in the early stages of growth, the least resistant organisms failing to divide.