In summing up the practicability of the Petroff method which is in reality a refinement and improvement upon well known methods, it has possibilities both from the standpoint of diagnosis and the study of the tubercle bacillus. It is not a difficult technique, but requires considerable attention to detail. The results should be better in larger series of cases carried on in laboratories where more time is available for close observation of the cultures during the early periods of development. It is the early transplanting of minute colonies even in the presence of contaminations which results in pure cultures.
As to the practical value of the method, my experience would lead me to conclude that where sputum is obtainable in suspected cases of tuberculosis in which the tubercle bacillus cannot be demonstrated, an opportunity for diagnosis would be missed if this technique were not applied. If the result is negative it means nothing; if positive an otherwise obscure case may be cleared up. The Petroff method offers an easy opportunity of isolating large numbers of pure cultures (Table I).