26 



MORPHOLOGY 



producing bacteria show great distortion in shape when the 

 acids produced are increased above a certain percentage. 

 Others show a change in shape when temperature is kept above 



FIG. 19. Involution forms. B. subtilis, water bacteria, Bact. aceti, Bact. 

 pasteurianum, bacteroids from root nodules, Bact. tuberculosis, Bact. 

 diphtheriae. All forms shown are very different from the normal forms. 

 After Fischer. 



the normal for any period of time, and others show change in 

 shape when food is lacking and excretory products have 

 increased to a high percentage. Too rapid reproduction may 

 cause aberrant shapes among some species. The condi- 

 tions which produce " involution forms " among bacteria also 



