664 CONTKlBUTlONS TO OUU KNOWLEDGE Of SOIL -FEhTILlTY,vi., 



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

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

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

 examination of the colonies ui)on the plates, were seen to be of the 

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

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

 pliagocytic propensities of the amcebaj, but it was moie probably 

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

 teria themselves. In this, as in the tirst 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 the kinds resistant to heat and disinfect- 

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

 other groups. 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-v-idgatus type. 



On conii»aring the numbers with tliose of tlie total bacteria, it is 

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

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

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

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

 ing forms. 



Upon noting tliat Buct. pulidum was one of the chief bacteria 

 in the un heated suspension, a series of portions of soil were seeded 

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



