96 MORPHOLOGIC VARIATION 



growth rate than during the resting phase, and that it becomes 

 increasingly greater with increased acceleration of growth; that any 

 external or internal factor which tends to speed up growth also tends 

 to increase the magnitude of this force. 



Clark and Ruehl noted that the large forms which they found 

 during the active growth phase were much more intensely stained 

 by the basic aniline dyes than were the "normal" forms found in 

 later stages of growth, and I have observed the same thing, the 

 intensity of staining being very striking. Eisenberg points out that 

 the Gram-staining of bacteria is variable with the age of the culture, 

 and that in very young cultures certain of the Gram-negative bac- 

 teria may retain the dye. Stearn and Stearn have shown that the 

 reaction of bacteria to acid and basic dyes depends upon the iso- 

 electric "zone" of the amphoteric protoplasm of which they are com- 

 posed, the difference between Gram-positive and Gram-negative bac- 

 teria being due to this difference in their iso-electric points. With 

 this information at hand we may generalize a bit and conclude that 

 in our "embryonic" bacteria the iso-electric "zone" is further on the 

 acid side of neutrality than is the case with the mature form, just 

 as in very old cultures it is further on the basic side. Gram-positive 

 organisms becoming Gram-negative, all organisms staining more 

 faintly with basic dyes, and some cells finally becoming stainable 

 with acid dyes like Congo red, as was pointed out in Chapter III. 



If we accept the diffuse nucleus theory for bacteria, is it not 

 plausible that this increased affinity for basic dyes is due to an 

 increased proportion of nucleoproteins distributed through the proto- 

 plasm? And is this not analogous to the high nucleus-protoplasm 

 ratio characteristic of the embryonic cells of higher organisms? 



Sherman and Albus (1923), as has been previously mentioned, 

 have found that young, actively growing cells of the colon bacillus 

 are much more susceptible to various injurious agents (heat, cold, 

 sodium chloride, phenol) than are older cultures. They also noted 

 that such young cultures were not susceptible to acid agglutination, 

 which may be correlated with the low iso-electric point of their 

 protoplasm as indicated above. They believe that these observa- 

 tions indicate a physiological difference between growing cells and 

 resting cells, that there is a "physiological youth" in bacteria analo- 



