Abstract
De Meio and Barron 1 state that neither their findings nor those of Ehrenfest and Ronzoni 2 support “Field, Martin and Field's 3 , 4 contention that dinitrophenol is active toward yeast only in its undissociated form.” Bearing in mind the fact that our “contention” relates only to studies on a pure culture of yeast, let us see to what extent the published data cited support the statement of De Meio and Barron.
Determination of the optimal concentration of 2–4 dinitrophenol (hereinafter DNP) at more than one pH level is essential for the decision of the point at issue. Ehrenfest and Ronzoni reported an optimal concentration of 0.36 mg. % DNP at pH 4.5 for their yeast. De Meio and Barron also reported work on yeast at one pH level only, viz: 6.64, and failed to state whether or not their dosage was optimal. Hence the published data cited afford no basis for the statement of De Meio and Barron, in fact the concentration of undissociated DNP corresponding to the optimum found by Ehrenfest and Ronzoni (assuming use of the sodium salt) is 0.00399 millimolar, which agrees very well with the values reported in the present paper for commercial yeast at other pH levels.
Moreover, De Meio and Barron used commercial yeast suspensions, which always contain several strains of yeast as well as numerous bacilli and cocci. Van Niel and Visser ‘T Hooft 5 have pointed out that pure cultures are essential for reliable work in microbiology. Conclusions drawn from experiments on heterogeneous populations cannot safely be regarded as generalizations, although it may chance that a conclusion drawn from work on pure culture will also apply in the presence of other species. The experiments reported below are a case in point, and show conclusively that undissociated DNP is the active agent in the stimulation or inhibition of yeast respiration in commercial yeast suspensions as well as in suspensions of pure culture. 3 , 4
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