UDDER INFECTION WITH STREPTOCOCCI OF THE SCARLET FEVER TYPE : III. THE INFLUENCE OF MILK ON THE GROWTH OF SCARLET FEVER STREPTOCOCCI.

The experiments indicate that milk filtered through a Berkefeld candle V or heated at 58°C. for 20 minutes when added to blood agar plate cultures interferes with the development of colonies of the scarlet fever streptococcus. The observed inhibition is proportional to the amount of milk. When the approximate milk dilution in the Petri dish is 1:20 or 1:25 growth of the organisms is completely suppressed or only a small proportion of non-hemolytic colonies develop. As the amount of milk is decreased the colonies become larger and their hemolytic zones more pronounced, although even when the final dilution of milk reaches 1:100 or 1:125 only colonies easily mistaken for the narrow zoned bovine streptococci appear. The effects upon the surviving organisms would appear to be transient since both the non-hemolytic colonies and those with small zones manifest the original hemolytic properties when transferred to other media. When scarlet fever streptococci are added in small quantities to milk heated at 58°C. for 20 minutes and incubated growth is inhibited. If the period is prolonged the streptococci are killed. On refrigeration of such mixtures some of the streptoccci are killed but others survive the test period.