544 Dr. We Al Walker: iniir [ Feb. 18, 
of these micro-organisms. This is the attitude which my experiments 
appear to justify. 
Abundant grounds exist in the known variability of chemical activity, and 
even of morphological characters which bacteria present, for regarding any 
simple test for specificity among these organisms with some suspicion, until 
it has been fully investigated under appropriate conditions. Under the 
influence of altered environment a considerable degree of adaptation would 
naturally be anticipated in these primitive organisms where the successive 
generations follow one another with such great rapidity as to reach in many 
cases even two or three per hour. But the remarkable degree of variability 
which bacteria do actually exhibit is perhaps not always kept sufticiently 
in mind. 
The great difficulties met with by Dreyer and FitzGerald (6) in 
ascertaining the precise conditions under which neutral red lactose bouillon 
could be made to yield uniform results in the differentiation of the 
B. typhosus, B. paratyphosus, and £B. colt showed incidentally that slight 
alterations in the composition of the culture medium are frequently sufficient 
to modify and even to reverse the chemical changes produced by these 
organisms in the medium in question. 
Again, Twort (7) has shown that the B. typhosus can be trained (in about 
two years) to ferment lactose in lactose peptone water. More recently 
Penfold (8) has noted a morphological change in the colonies associated with 
the development of this faculty, and has made important observations on the 
development or loss under suitable conditions of a number of other 
fermenting properties of the same organism. My own earlier observations (9) 
on the “immunisation ” of the same bacillus against its own specific immune 
serum (of the horse) by continued cultivation and sub-cultivation in that 
fluid demonstrated an adaptation of much greater complexity. This was 
associated with an increased virulence of the micro-organism, an increased 
resistance to the specific action of the anti-serum, and what appeared to be 
an actual production of specific anti-antibodies, showing a high degree of 
adaptability in the organism in question. 
Morphological variations of a greater or less degree are also common, 
and like the chemical variations they can be induced experimentally. 
Almquist (10) has described them both in J. typhosus and in V2. cholere; 
and Murray and I (11) have shown that in special media the B. typhosus can 
be made to assume a variety of novel appearances, in some of which it might 
readily be mistaken for a streptothrix. 
Both morphological and chemical variations of greater or less permanence 
are, therefore, very readily produced among bacteria. Accordingly a claim 
