1. Unsalted butter held at 21°C. showed a rapid increase in the number of bacteria it contained, whether it was held in the normal physical condition or with the serum largely separated. In general, the multiplication of bacteria was much more rapid when the serum was separated than when it was not.

2. Unsalted butter held at 7°C. also showed an increase in the number of bacteria contained, whether it was held in the normal physical condition or with the serum largely separated, but the increase was much less rapid than at 21°C. The multiplication was, in general, considerably more rapid when the serum was separated than when it was not.

3. Salted butter held at 21°C. tended to decrease in bacterial content, whether it was held in the normal physical condition or with the serum largely separated. In general, it appeared that the separation of the serum increased the rate of destruction of the organisms.

4. Salted butter held at 7°C. also tended to decrease in bacterial content, whether it was held in the normal physical condition or with the serum largely separated. At this temperature there was less of a tendency for the separation of the serum to increase the rate of destruction of the organisms than at 21°C.