Antagonistic Effects 269 



'l\iii,i-: (II. SiuvivAL OK I'Jucluri cilia coli. in Soil and l)i:\Kr.oi'MK\T 

 OF Antagon'Ists (from Waksmaii and W Inili) 



N'umluTs o( orf^aiiisms in I lioiisands |)cr gram (lr\\- soil. 



\uinl)or of Total 



liuuhatioM ICiiricliiiuMit.s K. coli Xumber of Nuiiihcr of 



of Soil witli K. roll Cells Haclcria .\nlaK'(>iiisls * 



days 



.. Few !»,]()(» t 



5 I fi , 800 



33 ."> i;JO 



127 11 40,000 Tj.TOO 



* An antagonistic colony is ()m<> surrounded hy a lialo of dissolwd K. coli ct'lls on the 

 plate. 



t Control soil, not receiving any enrichments. 



the corresponding bacteria; of citric, oxalic, and gluconic acids by 

 Aspergillus niger; of fumaric and lactic acid by Rhizopus nigricans; 

 of a number of alcohols by various yeasts, bacteria, and fungi; and 

 of certain phenols and quinones by various fungi. These substances, 

 as well as a great number of other compounds which, for lack of 



Fig. 104. Bacterial plates made from soil, showing clear zones surrounding colo- 

 nies of antagonistic organisms ( from Stokes and Woodward ) . 



more exact information, are usually designated as "lethal," "toxic," 

 or "growth-inhibiting" compounds, and more recently as "antibiotics," 

 have frequently been looked upon as protective metabolic products 

 formed by microorganisms in "their struggle for existence." Some 

 may play a highly significant part in the life of many organisms; the 

 role of others is still a matter of speculation. 



