EFFECT ON MORPHOLOGY OF MICROORGANISMS 251 



this phenomenon is due to the production and accumulation of metabolic 

 products injurious to growth. Nonspecific antibiotic substances were 

 demonstrated (692) in filtrates of bacteria. They not only injured 

 growth of other bacteria but prevented the production of the ectoplas- 

 mic antigen. These substances could be partly removed by the use of 

 adsorbents. 



The morphology of bacteria is greatly influenced by the presence of 

 other organisms or their antibiotic substances. In the case of diphtheria 

 bacteria this is accompanied by a reduction in virulence (417). The spe- 

 cific effect of the antagonistic B. mesenterkus upon the morphology of 

 antagonized bacteria has also been established (731). The antibiotic 

 substances produced by actinomycetes were shown (76) to affect the 

 growth of B. mycoides as follows: cell division is delayed; the cells be- 

 come elongated, reaching enormous size and assuming most peculiar 

 forms 3 spore formation or, with lower concentrations of agent, the ac- 

 tive substance is repressed j delayed nonspore-f orming variants are pro- 

 duced with a modified type of growth on nutrient media (Table 41). 

 The cells of bacteria subject to the action of streptothricin are greatly 

 enlarged, due to incomplete fission (287, 1031). 



Gardner (311) reported that concentrations of penicillin lower than 

 those required for full inhibition caused a change in the type of growth 

 of CI. welchn in liquid media. The majority of the cells became greatly 

 elongated, giving rise to unsegmented filaments ten to twenty times 

 longer than the average normal cells. The same was found to be true 

 of a number of other bacteria (Figure 27). Even gram-negative bac- 

 teria, which are relatively resistant to penicillin, showed the same ef- 

 fect. Many bacteria produced giant forms as a result of the autolytic 

 swelling and bursting of the elongated cells. It was recognized that 

 these changes were due to a failure of fission. Cell growth not accom- 

 panied by cell division underwent autolysis. Br. abortus and Br. meli- 

 tensisy which were not inhibited by penicillin even at i : i,000 dilution, 

 gave no enlargement of the cells but showed vacuolation even in lower 

 dilutions. CI. welchiiy which was inhibited by i: 60,000 penicillin, 

 showed filament formation in a dilution of i : 1,500,000. These obser- 

 vations were fully confirmed. All sensitive bacteria were shown (913) 

 to undergo lysis to a greater or less extent in cultures containing peni- 



