NUTRITION LABORATORY. 185 



been substituted for the silver-plated can. This has proved very successful 

 and can be prepared for use and cared for much more easily than the old 

 form of carbon-dioxide absorber. The blown-glass water-absorber devised 

 by Dr. H. B. Williams, formerly of Cornell Medical College, New York, has 

 proved of such value that a large number have been ordered and are now 

 in regular use in all of the respiration apparatus in this laboratory. Both of 

 these substitutions contribute very materially to the facility of manipulation 

 without a sacrifice of accuracy. 



A METABOLISM CAGE FOR DOGS. 



For use in experiments on dogs, it was necessary to devise metabolism 

 cages with suitable arrangements for saving the excreta. One of these cages 

 has been built by the construction force of the Nutrition Laboratory on the 

 plan devised by Prof. William J. Gies. 



RESPIRATION APPARATUS FOR DOGS. 



Many problems in the metabolism of animals may be satisfactorily studied, 

 or at least investigated in a preliminary way, by the determination of the 

 carbon dioxide alone without recourse to the more expensive and time- 

 consuming determinations of the oxygen consumed and heat eliminated. In 

 the two dog- respiration apparatus referred to in the last annual report, the 

 amount of carbon dioxide eliminated by the dog was determined by measur- 

 ing the increase of the carbon dioxide in the closed volume of air in the 

 sealed chamber. As this principle involved the use of an extremely accurate 

 gas analysis, the absorption system of the respiration apparatus for men was 

 combined with the dog-respiration chamber. By means of this absorption 

 system, a current of air is continually withdrawn from the chamber, the car- 

 bon dioxide and water absorbed, oxygen added to replace the amount used 

 by the animal, and the air returned to the chamber. The total amount of 

 carbon dioxide produced by the animal is weighed at the end of every half- 

 hour or hour period. By substituting a double-valve device at each end of 

 the absorption system, it is possible to keep the motor in continuous opera- 

 tion, since with a simple movement of the hand the air-current may be de- 

 flected from one set of purifiers to the other. With this device there is no 

 necessity of stopping the motor, disconnecting the purifying vessels, and 

 starting the motor again — a process which is liable to disturb the dog. This 

 absorption method of determining the carbon dioxide after careful tests has 

 been adopted for use with both the small and the large dog-respiration cham- 

 bers, and two series of experiments with dogs are now in daily operation in 

 this laboratory. 



The method of obtaining a graphic record of the muscular activity of the 

 dog has been somewhat modified the past year in such a way as to increase 

 its efficiency ; the great importance of such a record has been further demon- 

 strated in the recent researches. As is clearly shown by the kymograph 

 records, even in a state of rest there is considerable minor activity ; and when 



