176 



BACTERIA IN RELATION TO PLANT DISEASES. 



many facts as possible. Kendall, for instance, under the gelatin group has also 

 included action on dextrose as follows : 



The subject is now in the hands of a committee of the Society of American 

 Bacteriologists for consideration and recommendation, and criticisms are desired. 

 They may be sent to Prof. F. D. Chester, Wilmington, Del. ; Prof. F. P. Gorhain, 

 Providence, R. I., or to Erwin F. Smith, Washington, D. C. 



VALUE OF MORPHOLOGICAL CHARACTERS. 



Ebb and flow, growth and change, this is the order of the world. Living things 

 conform to a certain set of conditions and we say they are constant in structure 

 and function because the conditions are fairly constant ; change the environment 

 too much and they are destroyed ; change it essentially, ever so little, and the animal 

 or plant begins at once to respond to it. This is especially true of simple uni- 

 cellular forms. We can not, then, expect more than a moderate amount of constancy 

 in these low forms of life. If under slight changes of environment they are fairly 

 constant morphologically, it is all that we can expect, and in interpreting all 

 descriptions we must make due allowance for these slight changes which an author 

 may not have observed. 



There have been two extreme views respecting the morphology of the bacteria. 

 Bechamp, Hallier, Billroth, and Zopf stand for one extreme ; Koch's earlier views 

 for the other. To Hallier bacteria were only the developed plastids (protoplasmic 

 granules) of fungi, and under widely different forms we might have the same 

 organism functioning at one time as a harmless mold and at another as a micrococcus, 

 causing the dreaded cholera or some other human or animal disease. Bechamp's 

 microzymas were granules or fundamental elements more minute than the plant or 

 animal cell, granules out of which all life developed and which persisted in other forms 

 after the death of the cells. To Billroth all ordinary forms of bacteria, however dis- 

 similar they might appear, were but stages of one unique species, viz, his Coccobacteria 

 septica. Zopf did not carry his doctrine so far, but taught pleomorphism as a funda- 

 mental characteristic of the bacteria. To-day an organism might be a Micrococcus, 

 tomorrow a Bacterium or a Bacillus. Koch, on the other hand, insisted on the 

 fixity of forms. To him a bacillus was always the same thing, and the views of the 

 polymorphists were explained as the result of errors in technique, the confounding 

 of entirely different things. Koch's own methods were exact and his views had 



