C.-E. A. WINSLOW 



67 



1913) shows that in an untreated soil bacterial numbers remained constant, unaffected 

 by temperature variations between 5° and 40° C. ; while in a soil to which a slight 

 amount of toluene had been added marked increases occurred, at 20° and 30° and, 

 more slowly, at 5°-i2° C. 



Table V (from Hutchinson and MacLennan, 1914) is of special interest as demon- 

 strating the influence of lime upon a highly acid soil. It will be noted that o.i per cent 

 CaO produced a very slight stimulating action. The next three concentrations (0.2, 

 0.3, and 0.4 per cent) caused progressively increasing stimulation with a maximum 

 count on the ninetieth day. A strength of 0.5 per cent was somewhat less effective but 

 its influence was more prolonged, while a concentration of i.o per cent proved toxic at 

 first, with a later stimulation giving a higher count after the two-hundredth day than 

 was shown by any other sample. 



In this particular instance the effect of the lime upon the reaction of the soil no 

 doubt played an important part in stimulating bacterial multiplication. In general, 



TABLE V 

 Bacterial Content of Acid Soil Treated with Varying Amounts of Lime 



Days 



Control 



-|-o.i per cent CaO . . 



.2 per cent CaO . . 



.3 per cent CaO . . 



.4 per cent CaO . . 



0.5 per cent CaO . . 



-fi.o per cent CaO . . 



310 



5 

 3 

 13 

 63 

 71 

 77 

 337 



however, Russell and Hutchinson attributed the effect of heat and antiseptics upon 

 soils to the destruction of predatory protozoa. It seems quite possible that the in- 

 fluence of the treatment upon available foodstuffs (whether derived from the bodies 

 of protozoa or from other sources) may have been an even more important factor, as 

 in the case of Miquel's experiments cited above. 



In many other instances, it is certainly to the availability of the food supply, 

 rather than to the absence of inhibiting substances, that we must attribute the initi- 

 ation of the logarithmic growth phase. The amount of food required by the bacteria 

 may of course be exceedingly minute, particularly in the case of prototrophic water 

 forms. Kohn (1906) determined the minimal nutrient requirements for certain of 

 these types and found that they could develop in the presence of 198X 10 — '" to 198X 

 10 — ^^ per cent of glucose, 66X10—*^ to 66X10 — ^9 per cent ammonium phosphate. 

 With more fastidious organisms, however, a much ampler and more diversified diet is 

 necessary for maximal growth. Thus Tenfold and Norris (191 2) found that the maxi- 

 mum generation time of Bait, typhosum in i per cent peptone at 37° C. was 40 minutes, 

 but that when the peptone in the medium was reduced below 0.4 per cent the genera- 

 tion time increased and rose quite regularly with decrease in peptone content down to 

 0.2 per cent. In a o.i per cent peptone medium the generation time could be cut in 



