248 



PHYSIOLOGY OF BACTERIA 



meat extract. Rubner determined the nitrogen assimilated by the 

 bacteria cells as measure of the crop. His quite complicated method 

 of determining the nitrogen of the bacteria gave rather improbable 

 data, and his results are not only contradictory within themselves, 

 but also with the work of others who found the law of diminishing 

 returns established in bacteria. 



An experiment very similar to the theoretical discus- 

 sion above is that by Stern (1901) who grew yeast in a 

 mineral solution with 0.3% asparagin and increasing 

 amounts of glucose. Table 68 gives the crops from 

 100 c.c. of the medium. The yeast can grow without 

 sugar. Addition of sugar increases the crop, but the 

 increase per gram of sugar becomes smaller and smaller 

 as the food concentration increases, and above 15%, 

 no further gain is observed. 



Table 69. — Cells per Standard Loop of Micr. pyogenes in Meat 



Extract 



Another frequently quoted experiment is that by 

 Graham-Smith (1920) who grew Micr. pyogenes at 

 37°C. in meat extract of varying concentration. He 

 used the extract of 400 gm. meat in 1 liter of water, 

 filtered, without any other addition except neutraliza- 

 tion. Compared with standard nutrient broth, this is a 

 rather dilute medium. This meat infusion was diluted 



