664 CONTRIBUTIONS TO OUR KNOWLEDGE OF SOlL-FERTILITY,vi., 



The bacteria in the soils, seeded with living amoebae and bacteria, 

 multiplied very rapidly during the first day. This was due to the 

 quickly growing nature of the added microbes, which, from the 

 examination of the colonies upon the jjlates, were seen to be of the 

 coli-fluorescens type, and, among them. Bad. putidum was promi- 

 nent. The decline iu the numbers may have been caused by the 

 l^liagocytic projjensities of the amoebae, but it was moie probably 

 tiie result of the action of the bacteriotoxins secreted by the bac- 

 teria themselves. In this, as in the first experiment, there is no 

 evidence of any rapid increase in the ama^ba-free soil. 



A general observation of the behaviour of the bacteria in soils, 

 leads one to believe that tlie kinds resistant to heat and disinfect- 

 ants, are little influenced either by their own toxins or by those of 

 other groujjs. Such, however, does not appear to strictly hold, for 

 their growth is certainly restricted by the presence of toxins of 

 other groups, as the following approximate count of the rough, 

 opaque colonies upon the plates, shows. 



Experiment ii. — Bacteria of the Subtilis-vulgalus type. 



Uu comparing tlic numbers willi those of the tot;il l)acteria, it is 

 seen that tlie non-resistant have a decided iidiibiting action upon 

 the resistant bacteria, and, although the hitter increase as time 

 goes on, their multiplication is not so rapid in the presence as in the 

 absence of the toxins of the less resistant and more rapidly grow- 

 ing forms. 



Upon noting that lUui. pulidum^ was one of tlie chief bacteria 

 in the unhealed suspension, a series of portions of soil were seeded 

 with a pure culture of this organism, and, for the purpose of con- 



1 



