BACTERIOLOGY: E, O, JORDAN 
161 
bacterial cell and is evoked by proper stimuli. These latent qualities 
often play an important part in bacterial identification, and it is fre- 
quently impossible to recognize a given organism until it is brought into 
a particular environment and has given the appropriate response. Bac- 
teria are very sensitive to slight chemical differences in their surroundings 
and many alleged instances of variabiHty in bacteria are simply differ- 
ences in response evoked by variations in the composition of culture 
media. Herein lies the justification for the attempts at standardiza- 
tion of culture media and the maintenance of exact uniformity in the 
conditions selected for bacterial growth. The true latent character ap- 
pears promptly and typically when the suitable conditions for its mani- 
festation are afforded, and not under other circumstances. I have in 
my laboratory a culture of a bacillus discovered by one of my students 
(M. Didlake, CentralhL Bakt. II, 15, 193, 1905) that gives a brilliant red 
pigment in agar prepared from the soy bean, but fails to produce the 
pigment upon the ordinary meat broth peptone agar or upon any other 
medium tested. This is a clear case of a latent characteristic and is to 
be ranked with the fermentation of rare carbohydrates — as rhamnose 
by the paratyphoid bacillus — by microorganisms that in nature rarely 
if ever come in contact w'th the substances that they unhesitatingly 
attack. 
What are called environmental modifications are sometimes hardly to 
be distinguished fundamentally from the phenomenon just under con- 
sideration. In a sense these modifications depend upon the possession 
of an innate capability for response to a definite environment, and as 
such must be regarded as expressions of latent characteristics. 
Such modifications in the higher forms of life are typically the effects 
of use and disuse, of a more or less abundant food-supply or of chmatic 
factors. One important difference between such modifications and the 
bursting into bloom of latent characteristics is that environmental in- 
fluences of the nature indicated tend to produce similar results in different 
organisms. Among bacteria in general, latent characteristics are more sus- 
ceptible of demonstration than environmental modifications. It is often 
difficult in practice to distinguish genuine environmental modifications 
from adaptations due to selection, although the phenomena are totally 
distinct. If one-half of an alpine plant be set in a low altitude garden, 
the other half being left in its original habitat, differences will arise which 
may be reasonably ascribed to environmental modification. With bac- 
teria, experimentation of this sort is not so simple. The enormous num- 
ber of generations through which a given culture of bacteria can pass in 
