250 



PHYSIOLOGY OF BACTERIA 



dilutions. This is entirely in agreement with the theory 

 (p. 246) and is graphically shown in Fig. 25. 



The total crop at the different concentrations shows 

 the following relative values : 



There is a general parallelism between food and crop, 

 but it is not a direct proportion between the two. While 

 the food concentration drops from 100 to 10, the crop 

 drops only to 17. Or, while the food concentration is 

 increased from 10 to 100, the crop increases from 10 

 to only 61. 



This is the well-known '4aw of diminishing returns." 

 It is quite evident also in the yeast experiment described 

 in Table 68 where the increase in growth became smaller 

 for each additional gram of sugar. 



There seems to be, for some bacteria at least, a limit 

 of food below which they do not multiply at all. Car- 

 penter and Hucker (1927) give a number of such exam- 

 ples. Peltier's data (p. 207) also show a very decided 

 drop when the milk is diluted farther than 1:16. The 

 problem of growth in very dilute media does not seem to 

 have been investigated to any extensive degree though 

 the bacteriology of surface waters, city water supplies, 

 and even of soil would be greatly benefited by such an 

 investigation. 



