1. The principal sources of streptococcic infection, aside from clinical cases, are apparently normal cows which carry the virus in the udder.
2. These carriers may be grouped as follows: (a) those that have been infected recently and have not yet developed symptoms; (b) those that have suffered from inflammation of the udder and after recovery still harbor streptococci; (c) those that have had no clinical history of mastitis. There is some evidence to lead one to regard the latter group as naturally immune.
3. A milker may readily carry streptococci on his hands from an infected to an uninfected cow.
4. The vaginae of 34 of the 64 cows examined contained non-hemolytic streptococci. Of the 34 strains isolated 32 differed in their cultural characters and agglutination affinities from those associated with mastitis. The other two strains may be regarded as of etiological significance.
5. In no instance have hemolytic streptococci been isolated from the vagina.