160 
BACTERIOLOGY: E. O. JORDAN 
There remains of course the problem of identifying the free activator 
in the medium of the sperm suspension by its only known mode of opera- 
tion, that of fertilizing the ovum. This problem, over which several 
investigators have broken their weapons, appears in a somewhat differ- 
ent Hght as a result of these experiments; and new experiments should 
therefore be undertaken. 
VARIATION IN BACTERIA 
By Edwin O. Jordan 
DEPARTMENT OF HYGIENE AND BACTERIOLOGY, UNIVERSITY OF CHICAGO 
Read before the Academy, December 9, 1914. Received January 15, 1915 
The bearing of slight physiological differences upon the classification 
of bacteria and upon the phenomena of infection has made the occurrence 
of variation among bacteria fully as conspicuous as in the higher forms 
of life. During the past ten years many observations have been re- 
corded upon the extent and nature of bacterial variabiHty. In these 
studies some confusion has arisen through the difficulty of distinguishing 
true variations from the development of latent characteristics, and from 
environmental modification. 
By the term 'latent characteristics' is meant those quahties or prop- 
erties that are dormant in the organism or cell and are manifested only 
in response to definite external influences. Thus, certain bacteria form 
spores in the presence, but not in the absence, of oxygen; some bacteria 
are known that develop conspicuous capsules when growing in the ani- 
mal body, but lack these envelopes in part or altogether in artificial 
media; according to Wright, animal fluids seem to be essential for the 
production of the characteristic clubs of Actinomyces colonies. The 
sudden appearance in this way of a definite morphological character 
cannot be looked upon as an instance of variation. Such a manifesta- 
tion is merely an immediate response to changed conditions of life and 
is of exactly the same kind as the marked difference in the aquatic and 
terrestrial forms of Polygonum amphibium referred to by DeVries, or 
as shown in the transformation of the shrimp Artemia salina into what 
some writers consider another species, Artemia milhausenii, when the 
former is transferred to water of a greater degree of saltiness. In no 
sense is the awakening of such a dormant character to be confounded 
with true variation. In other words the power to produce certain struc- 
tures or certain physiological effects exists ready formed in the specific 
