358 
At this time I wish to bring to your at- 
tention some of the lines along which we 
are making little progress, I believe, be- 
cause of the false security which we are 
taking in our standard methods. 
First, suppose we consider our ordinary 
culture media. We have drawn up ridicu- 
lously exact procedures for mixing and 
boiling and filtering and titrating our 
broth, agar and gelatin, and when we are 
through we believe we have a standard, 
uniform product. But indeed it is not so. 
Not only are the results obtained in differ- 
ent laboratories unlike, but two lots of the 
same medium made at different times in 
the same laboratory are extremely unlike, 
when measured by the delicate physiolog- 
ical properties of organisms which respond 
to the slightest of chemical differences. 
Far better, it is true, are the results se- 
cured at the present time by the use of 
standard methods, than before their intro- 
duction, and I do not for a moment want 
to deery our standard methods, but I 
simply want to warn against the false se- 
curity which their use may give. For 
however careful we may be in the process, 
the final result can never be uniform as 
long as the ingredients used are themselves 
variable. No medium can be standardized, 
that is, can be exactly duplicated at 
another time or place, if it contains such 
variable materials as beef extract, either 
freshly made or commercial, peptone, gela- 
tin, agar, blood serum, bile, ete. I am in- 
clined to think that in order to get uniform 
results, particularly in our study of the 
delicate physiological properties upon 
which we depend so largely for the differ- 
entiation of bacterial species, the time has 
come for us to abandon altogether the use 
of all complex and variable animal and 
vegetable products, and in their places to 
substitute materials of definite, known, 
chemical composition. From my work of 
SCIENCE 
[N.S. Vou. XXXV. No. 897 
the past few years I am led to believe that 
for every organism it is possible to prepare 
a syuthetic medium containing chemically 
pure salts, upon which these organisms will 
grow and grow well. Such a medium as 
this we are able to duplicate exactly any- 
where and at any time. 
In the past we have been inclined to 
think that the physiological properties of 
many organisms were too variable to be of 
much use in species determination. I am 
coming more and more to think that it is 
not so much the properties of the bacteria 
which are variable as the environment 
in which we have attempted to study them. 
We talk about rejuvenation of organisms 
to restore them to normal conditions. Our 
attempts at rejuvenation are attempts to 
make normal organisms adapt themselves 
in short order to an abnormal environ- 
ment. Could we but supply the proper en- 
vironment we should find the organisms 
responding in an entirely normal and uni- — 
form manner. It is the environment, our 
culture media, that need rejuvenating and 
not the organisms. This rejuvenation 
will come about, I believe, through the 
adoption of synthetic media of absolutely 
known chemical composition. Then the 
physiological properties of organisms will 
come into their proper place in species 
differentiation, for then we can substitute 
the exact qualitative and quantitative 
tests of the chemist for the inexact de- 
termination of the present-day bacteriol- 
ogist. 
There is scarcely a physiological prop- 
erty of the bacteria that is to-day accu- 
rately measurable. Variations in the 
media are so great that measurements at 
present amount to nothing. Chemistry 
advanced to its present position as a sci- 
ence only when it became quantitative. 
Lord Kelvin said: that ‘‘When you can 
measure what you are speaking about, and 
