228 



Journal of Agricultural Research 



Vol. XIII. No. 4 



TabIvB II. — Bacterial flora of cheese made in the dairy division according to the Roquefort 

 method. Num.ber of organisms per gram of cheese 



Cheese 

 No. 



1732... 

 1732... 

 1732... 

 1732... 

 1732... 

 1732... 

 96.115. 

 1732... 

 1732... 

 1732... 

 1732... 

 1732... 

 1732... 

 1789... 



1754. ■■ 

 1727... 

 96. 121. 

 96.17.. 

 96. 124. 

 96. 125. 

 162I . . . 

 160I. . . 

 1590... 

 96. 12. . 

 96. 113. 

 96. 129. 



Age. 



Streptococcus 

 laciicus. 



These four samples 

 were taken at pro- 

 gressive stages of 

 J the cheesemaking. 



1 day 



2 days 



3 days 



4 days 



6 days 



8 days 



12 days 



16 days 



23 days 



25 days 



35 days 



38 days 



44 days 



48 days 



2I/2 months 



3 months 



2,% months 



3)^ months 



4 months 



4>^ months 



6 months 



6y^ months 



10, 000, 000 



20, 000, 000 



6, 500, 000 



9, coo, 000 



100, 000, 000 



10, 000, 000 



10, 000 



1 , 000, 000 



1 , 000, 000 



100, 000 



100, 000 



100, 000 



Cheese 

 streptococci. 



100, 000, 000 



5, 000, 000 



100, 000, 000 



100, 

 3i> 



000, 

 000, 



000 

 000 



. 000, 



i 300. 



, 000, 



120, 



I 000, 



40, 



10, 



100, 



000 

 000 

 000 

 coo 

 000 

 000 

 000 

 000 



Bacterium 

 bulgaricum. 



10, 000 

 14, 000, 000 



100 

 1 , 000, 000 



000, 000 



1 50, 000 



, 000, OCO 



170, OCO 



470, 000 

 I, 000 

 I, 000 



300 

 , 000 



100, 000 

 , 000, 000 



400, 000 



100, 000 



10, 000, 000 



2, 500, 000 



40, 000 



I, 000 



During the manufacturing of the cheese the Streptococcus lacticus 

 which had been added as a starter was the only organism present in 

 sufficient numbers to appear on the plates. These organisms gradually 

 disappeared, and on the twenty-fifth day their numbers had so dimin- 

 ished that they no longer appeared on the plates. 



A normal Roquefort cheese contains 4 per cent of sodium chlorid 

 (NaCl) in 40 per cent of water, which can be regarded as a 10 per cent 

 brine (<?). An experiment was carried out to show the effect of a high 

 concentration of salt on Streptococcus lacticus. Flasks of milk were 

 inoculated with 5. lacticus, incubated at 30° C. for about five hours, 

 when sodium chlorid was added to make a concentration of 10 per cent. 

 In five days all the organisms had been injured so that inoculations 

 into tubes of litmus milk gave no growth. Later, a hardier strain of 

 5. lacticus treated in the same manner was killed by the 10 per cent salt 

 solution between the tenth and the seventeenth days. This experiment 

 explains the complete disappearance of 5. lacticus from Roquefort cheese 

 during the first few weeks of ripening. 



In the ripening cheese the cheese streptococci had multiplied to 

 100,000,000 per gram on the second day. A 6-months-old cheese still 

 contained 10,000,000 of them, which demonstrates their hardiness in 

 respect to a high concentration of the salt, quite unlike the sensitive- 

 ness of S. lacticus. 



