66 



THE RISE AND FALL OF BACTERIAL POPULATIONS 



dium but that bacteria in more or less stable equilibrium in the water of a spring or 

 well should increase many thousand fold (see Fig. 2) merely because a portion of 

 the water in which they are living is placed in a sample bottle (even without any in- 

 crease in temperature, as Whipple's data show) is far more difficult to explain. And 

 the fact reminds us how subtle are the factors which constitute a bacterial environ- 

 ment. 



Similarly, it is of interest to note the observation of Jordan (1926) that fresh hu- 

 man feces (containing already 75,000,000 bacteria per gram) show an enormous fur- 

 ther increase on storage, sometimes reaching several hundred times the original figure 

 after a few days. This increase is mainly due to multiplication of Bad. coli and occurs 

 at 10° and 20° as well as at 37°C. It is suggested by Jordan that the multiplication 

 may be due to the loss of specific inhibitory influences present in the lower intestine. 



Miquel attributed the rapid growth in a new medium to the absence of toxic 

 products of prior bacterial growth and found that boiling destroyed the "toxicity" of 



TABLE IV 



Bacterial Content of Normal and of Toluene-treated 

 Soil at Various Temperatures 



Temperature, °C 



5- 1 

 20. 



30- 

 40. 



50- 



Bacteria, Millions per Gram 



Untreated Soil 



5 Days 



27 Days 



58 Days 



Toluened Soil 



5 Days 



8 

 50 

 43 

 12 



2 



27 Days 



27 



30 



24 



4 



58 Days 



28 



30 



31 

 6 



water rendered unsuitable for growth by such earlier development. When we transfer 

 from an old culture to a new sterile tube of the same medium in the laboratory, this 

 factor must play a major part, since, as I shall point out in discussing the phase of 

 crisis, growth is often undoubtedly checked in old cultures by the accumulation of 

 acids or other toxic products. Cohen and Clark (191 9) found for Bad. coli in broth a 

 generation time of 27 minutes at pH 5.0 while at pH 8.9 the time increased to 46 min- 

 utes and in the acid range at pH 4.6 there was a decrease instead of an increase. For 

 the multiplication following collection of a water sample such an explanation seems, 

 however, clearly inadmissible, and the favorable effect of boiling is probably due 

 chiefly to the alteration which heat produces in certain of the foodstuffs which are 

 present. 



The work of Russell and Hutchinson (1913), Hutchinson and MacLennan (1914), 

 and Buddin (1914) from the Rothamstead Experiment Station and the similar studies 

 of Truffant and Bezssanoff (1922) in France have given us some important data in re- 

 gard to the multiplication of bacteria in soils. They found that the treatment of a soil 

 by moderate heat or by mild antiseptics caused a marked secondary increase in bac- 

 terial numbers and crop fertility. Thus Table IV (from Russell and Hutchinson, 



