40 MORPHOLOGICAL CHANGES DURING GROWTH 



of discrete granules (chromidia), irregular filaments, branched rods, or one or more 

 large masses of nuclear substance. Even different stages of mitosis have been de- 

 scribed by Mencl', Guilliermond^, and others. 



Beyond this point it is difficult to analyze the large number of observations which 

 various authors have presented as evidence of the existence among the bacteria of the 

 more complex methods of reproduction commonly found among the Protista. Many 

 authors describe various budlike structures, large bizarre forms, minute deeply stain- 

 ing bodies, and imperfectly stained masses, and have read into these observations cer- 

 tain sequences which, it seems to me, have not been adequately proved. The diffi- 

 culty of demonstrating genetic descent with organisms so minute is apparent. 

 Since, however, the purity of the culture is so completely essential for evaluation of 

 these observations, should we not insist that some method of single-cell isolation be 

 employed as a basis for work of this sort, even though successful transplants can be 

 obtained in a very small percentage of the attempts? Most of the work on "life- 

 cycles" in bacteria has not been carried out with this foundation, and many of the 

 observations are inadequate as experimental proof of developmental cycles, however 

 much the notion may appeal philosophically. A few papers presenting observations 

 in the field of soil bacteriology cause the scales to tip rather sharply toward the "life- 

 cycle" side. Notable recent contributions are those of Thornton and Gangulee^ with 

 Bacillus radicicola and Cunningham and Jenkins^ with B. amylobacter . Unfortunate- 

 ly, neither of these papers is based on single-cell isolations. 



That bacteria, even among the Eubacteriales, do at times reproduce by means 

 other than equal fission seems to me to be definitely proved. Some of the best ob- 

 servations in this connection have been made by Hort,^ who has studied a number of 

 the common pathogens, watching the development of the organisms by means of a 

 combination of single-cell technique and warm stage growth. He has demonstrated 

 that, under adverse conditions, some strains of the colon-typhoid group reproduce by 

 budding, by branched Y-shaped forms, and by the production of large aberrant forms in 

 which the fragmented chromatin appears as deeply staining granules. These granules 

 are subsequently extruded and are small enough (0.1-0.2 micron in diameter) to pass 

 through the coarser bacterial filters. He watched the subsequent development of 

 these "gonidial bodies" into typical baciUi. He avoided the assumption of any defi- 

 nite life-cycle, but emphasized his demonstration that methods of reproduction other 

 than binary fission occur among bacteria, and that the irregular bodies cannot be 

 considered involution forms since he has shown that they reproduce actively. 



The essential details of Hort's observations were confirmed by a specially ap- 

 pointed committee consisting of Leishman, Adami, Farmer, and Harvey.^ 



With a somewhat similar technique Gardner^ has also described reproduction at 

 each of the three growing points from Y-shaped organisms in six members of the colon- 



' Mencl, E.: loc. cil. " Guilliermond, A., loc. cil. 



3 Thornton, H. G., and Gangulee, N.: loc. cit. 



^ Cunningham, A., and Jenkins, H.: loc. cit. 



sHort, E. C.: see various works cited previously. 



^Leishman, W. B., Adami, J. G., Farmer, J. B., and Harvey, D.: /. II yg., 18, 380. 1920. 



' Gardner, A. D.: /. Falh. &° Bad., 28, 189. 1925, 



