184 REPORTS ON INVESTIGATIONS AND PROJECTS. 



Among the important points developed this year was the desirability of 

 using a thermostat for maintaining an absolutely constant temperature inside 

 the calorimeter chambers when they are not in use. With this constancy of 

 temperature, any one of the calorimeters may be opened at a moment's no- 

 tice, a subject placed inside, and an experiment immediately begun without 

 the delay incidental to a preliminary warming or cooling of the chamber. 



As a result of the extensive research in body- temperature measurement 

 made by Mr. E. P. Slack, of this Laboratory, an arrangement of thermo- 

 elements has been applied to the calorimeters for measuring the rectal tem- 

 peratures of subjects, so that a measurement of the body temperature may be 

 obtained with great accuracy simultaneously with the measurement of the 

 products of metabolism. 



BICYCLE ERGOMETER. 



The bicycle ergometer described by Benedict and Carpenter* was so suc- 

 cessfully used in the respiration-calorimeter experiments on muscular work 

 at Middletown, Connecticut, that a duplicate of the apparatus was considered 

 desirable for the Nutrition Laboratory. This has been constructed in the 

 machine-shop during the past year, and at present is undergoing rigid and 

 critical tests. 



RESPIRATION APPARATUS. 



The small respiration apparatus for nose or mouth breathing, which has 

 been in process of development in the laboratory for the past three years, 

 has proved so successful that several have been constructed during the 

 winter and are now in active and continuous use. 



Method of determining oxygen. — The amount of oxygen admitted to the 

 system of the respiration apparatus was determined originally by measuring 

 the loss in weight of a small cylinder of the highly compressed gas. This 

 method was very successful and is recommended for isolated plants. Re- 

 cently, however, a new method has been used in which the amount of oxygen 

 admitted to the system is recorded on an extremely exact gas-meter, com- 

 pletely immersed in water and carefully calibrated by special tests. By this 

 means the weighing of the oxygen cylinders can be dispensed with, thus 

 greatly facilitating the manipulation of the apparatus, with no sacrifice of 

 accuracy. The results have been so satisfactory that this method of meas- 

 urement will in future be used on all of the respiration apparatus in the 

 laboratory. 



Absorbers for carbon dioxide and zvater. — As a logical outcome of the 

 development of the absorbing system used in connection with the large respi- 

 ration chamber of the calorimeter, we have been accustomed to employ a 

 silver-plated can containing soda lime for absorbing carbon dioxide, and the 

 lower part of a so-called Kipp generator filled with pumice-stone to absorb 

 the water from the air-current. Recently an ordinary wide-mouth chemical 

 bottle, fitted with metal pipes passing through a solid rubber stopper, has 



* Benedict and Carpenter : U. S. Dept. Agr., Office Expt. Stas., Bui. 208, 1909. 



