



RESPIRATION CALORIMETER AND EXPERIMENTS. 257 
of the physiological difficulties in the way of absolutely accu- 
rate results, and the evident possibilities of minor errors in the 
purely chemical and physical determinations, this agreement 
seems to us very satisfactory as marking a stage in the devel- 
opment of the apparatus and methods, and sufficient to warrant 
some extended series of experiments upon various questions 
connected with the laws of nutrition. Such experiments are 
now being carried out. Efforts are being made at the same 
time to eliminate part at least of the experimental errors. At 
present these are chiefly in the direction of improvement of 
methods of sampling and analyzing the food materials and 
excretory products, the finding of minor sources of error in 
the determinations of carbon, hydrogen and heat given off in 
the respiration chamber, and the direct determination of the 
oxygen of income and outgo. Minor alterations are also being 
made in the apparatus and the methods of its manipulation by 
which it is hoped that somewhat greater accuracy may be 
secured. 
THE CONSERVATION OF ENERGY IN THE LIVING ORGANISM. 
It is commonly assumed that the law of the conservation of 
energy applies in the living organism; that, in other words, 
the metabolism of energy in the plant and in the animal takes 
place in accordance with the same physical laws that obtain 
elsewhere. While there seems no reason to doubt this princi- 
ple it has lacked the final proof of exact experiment. Gradual 
approaches toward such demonstration have been made from 
time to time. Meanwhile, awaiting this absolute demonstra- 
tion, physicists, chemists and physiologists generally, if not 
universally, assume the correctness of the principle.* The 
experimental inquiry of later years has brought results which 
strongly confirm it. This is notably the case with the experi- 
ments of Rubner.+ In these, which were made as a study of 
the source of animal heat, the subjects were two dogs weigh- 
ing about 5 and 12 kilograms respectively. In some of the 
experiments the animals fasted; in others they had lean meat 
. . a ° . 
* For an early discussion of the subject see J. R. Mayer, Dze organtsche Bewegung 11% 
threm Zusammenhange mit dem Stoffwechsei; Heilbronn, Rd OS 5h aware : 
See also Rubner, Die Quelle der thierischen Warme, Zeitschrift fiir Biologie, 30, 1894, 
pp. 73-86, and W. O. Atwater, Methods and Results of Investigations on the Chemistry 
and Economy of Food, Office of Experiment Stations of the U. 8. Department of Ag- 
riculture, pp. 113-135. 
Ta,0C.Cit. 
