In the present paper are given the results of studies on the respiratory and glycolytic metabolism of Pneumococcus Types I, II, and III, and of the R forms derived from these. The metabolism of the S and R forms are compared, and the relationship between changes in virulence, changes in chemical constitution, and changes in metabolism is discussed.

1. There is no respiration in Ringer solution unless sugar is added.

2. The pH (7.8) that is optimal for growth of pneumococcus is also the pH at which the maximum respiration occurs.

3. The intensity of respiration varies with type in the strains used. The respiratory capacity of Type I is 56 per cent of that of Type III, which in turn is 71 per cent of that of Type II.

4. The anaerobic glycolysis is approximately the same for all three groups.

5. Pneumococcus Type I is capable of aerobic glycolysis.

6. Pneumococcus Types II and III do not effect glycolysis aerobically.

7. The energy set free in respiration is considerably greater than that set free in glycolysis.

8. The oxidation quotient for lactic acid is of the same order as found by Meyerhof in muscle and by Warburg for mammalian tissues.

9. The respiratory capacities of Types I and III are changed on conversion of the smooth to the rough form. (a) For Type I the respiration is increased 110 per cent. (b) For Type III the respiration is diminished 45 per cent. (c) For Type II there is only a slight diminution in respiratory activity (16 per cent).

10. The anaerobic glycolysis is increased about 25 per cent on the average for all R forms irrespective of type derivation.

11. Type I on being converted to the R form, loses its capacity for aerobic glycolysis.

12. Type III, on being converted to the R form, gains the capacity for aerobic glycolysis.

13. The oxygen consumption by Pneumococcus compared with that of the human tubercle bacillus and of mammalian tissue, for the same time intervals, weight for weight, is as follows: (a) Pneumococcus Type I consumes thirteen times as much oxygen as does the tubercle bacillus (H37). (b) Pneumococcus Type II consumes thirty-four times as much oxygen as does the tubercle bacillus. (c) Pneumococcus Type II consumes over twenty times as much oxygen as does isolated rat kidney tissue, and almost 100 times as much oxygen as does isolated dog muscle.

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