218 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1926 
in a candle. This was one of Lavoisier’s great contributions to 
science. A bacterium could obtain no more energy in burning its 
foodstuffs than a guinea pig or any other organism. 
Knowing the oxygen consumption of an animal and its food, we 
can calculate its heat production, and this “method of indirect calo- 
rimetry ” gives results in surprising agreement with direct measure- 
ment of heat production in a calorimeter. Applying this method 
to luminous bacteria, which were fed upon 60 per cent glycerin and 
40 per cent peptone, each liter of oxygen consumed should produce 
4,840 gram-calories or 3.4 gram-calories per milligram of oxygen con- 
sumed. We have only to measure the oxygen consumed by the bac- 
teria to find how much energy is supplied by the food during lumi- 
nescence. 
Converting energy from milligrams of oxygen utilized and lumens 
of light emitted into the same units, calories, the over-all efficiency of 
a bacterium turns out to be 0.16 per cent. ‘This tells us the percentage 
of the energy necessary to run a bacterium which appears as light. 
It does not give us a true picture of the efficiency of the light-produc- 
ing reaction, for much of the oxygen consumed is used by bacteria 
for processes which have nothing to do with luminescence. It can be 
shown by other experiments that certainly only one-sixth of the 
oxygen is used in luminescence, and probably much less than this. 
Using the figure, one-sixth, brings the efficiency of the bacterium to 
nearly 1 per cent, a figure twice as great as that for over-all efficiency 
of the best incandescent lamp. 
While the extravagant claims for total efficiency of luminous ani- 
mals are not confirmed by my investigations, nevertheless the value, 
which I regard as a minimum value, is sufficiently high to warrant 
further inquiry into the process by which animal light is produced. 
We usually find that living creatures have developed very economical 
ways of doing things, and one would like to know what the total 
efficiency of luminous animals, far brighter than luminous bacteria, 
might be, if we could separate completely the light-producing process 
from the other energy-consuming processes of the animal. 
Such creatures as I have described offer problems of fascinating 
interest. The chief appeal is to the intellect, a study in pure science, 
in a field whose boundaries touch biology, physics, and chemistry. 
Advance will be made when the ever-widening waves of knowledge 
in each science meet and reinforce each other. Cooperation between 
the sciences is sure to bring more and more fruitful discoveries. I 
have endeavored to point out some of the interlocking connections 
in the field of light. Princeton is fortunate in having research on 
this important subject well under way in five fundamental sciences 
and a future program which we hope may be carried out with an 
adequate endowment for pure scientific research. 
