LOUIS FREEDMAN 7 



was adjusted to an alkaline range (Pn of 7.4-7.8), a more uni- 

 form growth of the microorganism was obtained. An added 

 factor may be the possible presence in autolyzed yeast of sub- 

 stances which are toxic to the specific organism. The above 

 results are given in detail in table I. 



TABLE I. 

 Growth of streptococci on various media. 



No. MEDIA Growth 



1. 10 cc. Undecolorized beef -heart infusion ................... 



2. 10 cc. Decolorized beef -heart infusion 



3. 10 cc. Glucose-salt solution (G. S.) 



4. 10 cc. D. I.-G. S. solution 



6. 10 cc. D. I.-G. S. solution, containing 1% peptone 



6. 10 cc. G. S. solution containing 1% peptone ................. 



7. 10 cc. 1% peptone solution alone ........................... 



8. 9 cc. D. I.-G. S. + 1 cc. 5% autolyzed yeast ............... + 



9. 9cc. D. I.-G. S. + 1 cc. 6% autolyzed yeast (Pn 7.4-7.8)... + 



-}- + + Denotes profuse growth. 

 4- + " moderate " 



-f slight 



no 



EFFECTS OF THE SAME MEDIA ON THE GROWTH OF YEAST CELLS. 



For the test on the growth of yeast cells, we followed the 

 Funk-Dubin 2 method, which is the most convenient and which, 

 briefly, is carried out as follows : A yeast suspension is prepared 

 by shaking a loopful of a 48-hour pure yeast culture in 100 cc. 

 Nageli solution on a shaking machine for three hours. Duplicate 

 sets of tubes are prepared containing 



(1) 4 cc. yeast suspension + 5 cc. Nageli solution + 1 cc. water 



(2) 4 cc. yeast suspension + 5 cc. Nageli solution + 1 cc. of the 



solution to be tested. 



The tubes are incubated for 20 hours at 30 C., and the 

 fermentation is then stopped by heating the tubes in a water 

 bath to 75 C. The contents of the tubes are then transferred to 

 special centrifuge tubes, the bottom part of which is a capillary 

 2.5 cm. long and is graduated in millimeters. These tubes are 

 centrifuged for 15 minutes at about 2500 R.P.M., and the growth 

 of the yeast cells is read directly on the tube. The reading of 

 tube 1, which constitutes the blank, is subtracted from that of 

 tube 2 to give the net growth of yeast cells in millimeters. In all 

 tests, conditions were maintained which precluded the possibility 

 of bacterial contamination. 



