From the study of different tissue extracts as media for the growth of pneumococci used in an automatic transfer device, certain inferences are warranted:

1. Media made from calf lung or heart, or from horse skeletal muscle maintain virulence over a long period of time. Conversely, media made from calf spleen lead to a decrease in virulence.

2. Lung medium causes an increase in virulence of seven strains of pneumococci.

3. Virulence is maintained in normal horse serum; but, it rapidly decreases in immune serum, or in pneumococcus antibody solution, a finding which confirms the work of Stryker. Immune serum freed from protective antibody gives results similar to normal serum.

4. Rabbit medium made from the entire animal apparently is less suitable for the maintenance of virulence of pneumococci than medium made in the same way from guinea pig.

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