GENERAL FOOD RELATIONSHIPS— METABOLISM 75 



period when growth and death are equal, d-e] increased 

 death-rate, e-f\ uniform death rate, f-g ; followed b}' a slowing 

 down of the death and a stationary or resting period, g-. 

 The time intervals indicated in this diagram may be hours, 

 days, weeks, etc., depending on the organism, the environ- 

 ment, etc. 



The following table adapted from an experiment by 

 Henrici^ illustrates by numbers the growth and death of 

 bacteria : 



I II III 



Days of growth. Live bacteria. Total live and dead. 



1 2,790,000,000 2,555,000,000 



2 3,650,000,000 3,820,000,000 



3 3,200,000,000 4,760,000,000 



4 2,265,000,000 5,350,000,000 



7 760,000,000 5,760,000,000 



10 54,000,000 5,670,000,000 



14 8,700,000 5,600,000,000 



19' 1,610,000 5,380,000,000 



25 



A comparison of columns II and III shows the very great 

 diminution, dying out, of the bacteria which begins to be 

 evident in this experiment about the third day. 



Mutation.— The fundamental reasons why bacteria are 

 expected to vary with their environment have been alluded to 

 on page 50. With respect to the chemical environment it 

 is readily apparent that the change which might be sufficient 

 to modify the characteristics of a single organism is almost 

 infinitesimal. A coccus 1 ;u in diameter has a volume of 

 0.5236 by 10-^'^cc. The actual quantit}^ of any one of the 

 chemical substances present in such an organism, discussed 

 in Chapter VII, or of the elements composing them, could not 

 be detected by any known means. The great variety of 

 so-called "mutations" discussed in the literature of recent 

 years are understandable on the basis of change in the environ- 

 ment, though this, of course, does not explain tvhy they should 

 vary. That is still one of the secrets of living substance. 



Life Cycles.— A number of writers have claimed to see in 

 the changes observed in growing bacteria more or less com- 



1 Henrici, Arthur T. : Morphologic Variation and the Rate of Growth of 

 Bacteria, 1928, p. 170. 



