In the milk of herds “free” from streptococcus infection, the presence of staphylococci has been shown to accompany chemical changes in the composition and abnormalities of pH.

In mastitis control schemes, based on Str. agalactiae infection, cases of staphylococcus infection are missed because of suppression of growth on the routine crystal violet blood agar of Edwards. Further, as clinical cases of staphylococcus mastitis causing serious disturbance are comparatively rare, the subclinical type may be present to a considerable extent and yet remain unsuspected. Thus in herds free from streptococcus mastitis, we have found that in 428 “cowtests” staphylococci werefound in 21 %. No clinical case was observed, although careful records of all abnormalities of udders and milks were kept.

The data which we have obtained show that staphylococcus infection accompanies changes of chemical composition which may be of importance in the preparation of milk products, but before categorical statements can be made more observations are obviously necessary.