249. Studies on the methylene-blue reduction test II. Comparison between the old and the modified methods

Abstract

In order to compare the old and the modified methods of the methyleneblue reduction test, 185 samples of raw milk were examined. We followed Wilson's method absolutely, but included two tubes in each test, one of which was inverted and the other not.The results obtained and their interpretation agreed with the theoretical expectations given in our previous paper, and briefly outlined at the beginning of the present paper.It is found that the deviations in the reduction time, corresponding to a given initial number of cells, are smaller by the modified than by the old method, and that the average time of reduction is shorter.The smaller variation in the reduction time corresponding to a given number of cells at the beginning of the test is due probably to a more uniform distribution of the bacteria in the milk following the inversion of the tube. Wilson's suggestion that the shortening of the reduction time in the modified method is due to the stimulation of bacterial growth proves to be entirely correct. We obtained the average coefficients of multiplication in the old method of 0·660, and in the modified of 0·885.Our results confirm on the whole the positive value of the modification of the methylene-blue reduction test as suggested and worked out by Wilson.