CHEMICAL CHANGES loi 



their special food, or (2) by excreting products which are 

 injurious ; the latter is true antagonism. Thus Freudenreich 

 found that B. pyogenes fetidus (p. 72) prevented the growth of 

 the cholera spirillum, that Micrococcus roseus similarly inhibited 

 M. tetragenus, whilst B. pyocyaneus, phosphor escenSf and prodigio- 

 sus caused a change in broth which prevented the growth of 

 other species. Garre demonstrated antagonism by making 

 streak cultures of various bacteria on gelatine plates, in parallel 

 or intersecting lines.^ Lewek inoculated gelatine or agar with 

 equal numbers of different varieties, adjusted by counting and 

 appropriate dilution.^ K. B. Lehmann draws the practical 

 inference that in counting bacteria very dense plates should be 

 avoided. 



Symbiosis is the condition when two or more kinds of 

 bacteria act together and effect decompositions which neither 

 of them could do separately. Each may live independently, 

 but they thrive better and more continuously in company than 

 alone, and are said to be synergetic. Lehmann states that some 

 organisms ordinarily anaerobic can thrive on the admission of 

 air if certain aerobes be also present, which is one reason 

 accounting for the presence of anaerobes in oxidizing beds or 

 filters. 



The cause of symbiosis is generally found in each of the 

 organisms taking one part in a sequence of chemical actions.^ 

 Thus, Omeliansky, by pure cultivations, explained some results 

 that Adeney and others had previously noticed. When three 

 organisms, B. racemosus, 7iitrosomonas, and nitrobacter, are added 

 to bouillon, the first bacillus produces ammonia from the 

 organic nitrogen, the second converts it into nitrite, and the 

 third the nitrite into nitrate. The first change requires no 

 oxygen, the second requires some oxygen, and the final change 

 a still greater quantity. With a culture of the first two, nitrite 

 and no nitrate was produced. With a mixture of B. racemosus 

 and nitrobacter, ammonia was the only product, as the absence 

 of the nitrite-forming organism prevented the conversion of the 

 ammonia into food for the nitrifying organism. A mixture of 

 the two last species failed to determine the decomposition of 

 the original culture medium even after ten months. Otto 

 Ktinnemann * found that Burri and Stutzer's B, denitrificans L 



^ Corresp. fiir Schweizcr Aertzc, 1897. 



2 Centr. /. Bakt., vii., 107. '^ Kossowicz, Woch.f. Bmu., 1906, xxiii., 262. 



■* Landw. Versiichs Stat., 1898, 65. 



